シャドーイング練習: Every Networking Concept Explained In 20 Minutes - 動画で英語スピーキングを学ぶ
レッスンを作成中...
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In this video, I'm going to show you the essential networking concepts that every software engineer needs to understand.
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We will follow a simple approach, basically watch how one application grows from a single server to a complex cloud system
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and learn each networking concept exactly when it becomes necessary.
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So meet Travel Buddy.
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This is going to be our imaginary travel booking website.
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and we will see how its networking needs evolved over time
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and you'll understand why each networking piece exists and how it solves real problems.
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We also created a detailed handout that breaks down everything that I'm going to cover today.
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So make sure to grab it from the link below.
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It's completely free.
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So let's start at the beginning.
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When we first launched Travel Buddy, we had one server running our entire application application.
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Simple, right?
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But immediately we faced our first networking question.
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How do customers actually find our server on the internet?
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Every device connected to a network needs an identifier so that other devices can send data to it.
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And this identifier is called an IP address.
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Think of it like a house address for mail delivery.
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Without it, no one knows where to send anything.
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So our travel body server got a public IP address, which looks like this.
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This means any device on the internet can send a request to this specific number and reach our server.
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Now you may be thinking, do I need to remember numbers like 203,
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0, 100, 13, and 10 to reach a website?
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No, just like you don't memorize phone numbers anymore, we don't memorize IP addresses either.
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And this is where DNS comes in.
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DNS translates easy to remember names into IP addresses.
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So when someone types travelbuddy.com into their browser,
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DNS automatically looks up the IP address that will look like this and connects them to our server.
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DNS works like contacts in your phone.
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not type in the phone number, the actual phone number.
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You just tap on the name, like mom, and your phone finds the actual phone number in the background.
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Just like you type google.com and DNS finds the actual IP address behind that name.
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So now customers can find our server.
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Good.
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But here is the next problem.
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Our single server is now running three different things.
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the website that customers see, a database storing all the booking information, and a payment processing service.
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All three share the same IP address.
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So when the request arrives at our server, how will the server know which application should receive it?
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This is where ports solve our problem.
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Ports are numbered channels on a server, ranging from 1 all the way to 65,535,
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and each application listens on a different port number.
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So let's say this is how we set up our application.
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The website listening on port 80, which is standard for web applications or for a secure connection,
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there is a standard port for secure web application connections on port 443.
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Then we have a MySQL database listening on port 3306.
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That's a standard MySQL port.
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And then we have some custom payment service that we decided to run on port 1990.
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Now, when a customer visits travelbuddy.com, their browser automatically connects to port 80 or 443,
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and the server knows to send the traffic to the web application and not to some other program on the server.
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So think of it like apartment building.
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The building has one street address, that's the IP address, but inside the building, there are different apartment numbers, like the ports.
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Great, so that's taken care of.
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But now, we're growing and a new problem appears.
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Travel Buddy is now handling customer credit cards and some personal information.
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And having everything on one server creates a big security risk for us and for our users.
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Because if a hacker now broke into our server that runs all these applications, they get access to everything.
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To the database, to the payment service, everything.
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So we need to separate things.
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This is called network segmentation.
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And subnets let us divide our network into separate sections.
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Think of it like a hospital that has different floors and wings for different types of patients.
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like maternity ward on one floor, surgery on another to keep things cleanly separated.
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We do the same with our network.
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Let's say our front end servers, which are public facing go in subnet A, with this IP address range,
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application servers going subnet two with this IP address range and database servers go in another subnet.
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So now our network is divided.
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But wait, if the website is in one subnet and the database is in another subnet, how does the website talk to the database now?
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And this is where routing becomes necessary.
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Routing directs traffic between different network segments.
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When the website needs data from the database, the router will determine the path.
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So it's basically like a GPS for network data.
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It figures out how to get from point A to point B.
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But now we have a new problem.
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We've separated things into different areas, but what stops everything from talking to everything else?
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We've created separate rooms, but all the doors are now wide open and unlocked.
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Just because we can route traffic between subnets does not mean we should allow all traffic in all directions.
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And that's where firewalls become necessary.
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A firewall is like a security guard that checks every piece of traffic
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and decides whether to allow it based on rules that we set.
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We have host firewalls that protect individual servers.
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So we put firewall on the database server and create a rule
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that says only accept connections on port 3306 and only from IP addresses in the front end subnet.
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Anything else gets blocked.
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And we also have network firewalls that sit between subnets and filter traffic.
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So we may place one between the internet
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and our frontend subnet with a rule saying allow incoming traffic on port 80 and port 443,
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but block everything else.
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So if we have another program or application running in front of subnet on a different port, it will be blocked right away with this firewall rule.
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So this layered approach means that an attacker has to get through multiple security checkpoints like the network firewall,
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then the host firewall to actually do any damage because security is always layered.
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With firewalls in place, we have now created secure zones in our network.
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But another problem is about to appear.
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Travel buddy is growing fast.
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We now have 50 backend servers in a private subnet for security.
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And these servers have private IP addresses like 10 0 2 5,
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10 0 2 6, 10 0 2 7 and so on.
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So private IP addresses work inside your own network, but they cannot communicate directly with the internet.
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It's like having an internal extension number at the company.
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You can call other extensions inside the building, but you can't dial an extension number from your home phone from outside the building, from your home office.
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But our backend servers do need to reach the internet sometimes to download software updates,
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to connect to external payment APIs maybe, or to send data to third party services.
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So how do we solve this problem?
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Because now we have them secured so that nobody can just directly reach them from internet, they cannot reach internet either.
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And we can't give each server a public IP address because first public IP addresses cost money
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and we need to manage them and we would now need 50 of them.
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Well, that's where NAT or network address translation comes in.
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So NAT basically allows multiple devices with private IP addresses to share one public address when accessing the internet.
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So here's how it works.
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When backend server 10.0.2.5 wants to reach an external website to let's say download updates for a database,
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it sends a request to the net device.
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The net device replaces the private source address with its own public IP address and sends the request out to the internet.
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When the response comes back, the net device remembers all this response is meant for server 10.0.2.5 and sends it to the right place.
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So think of it like a receptionist at an office.
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When an employee needs to make an external call, they go through the company's main phone line.
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The receptionist places the call using the company number and then routes the response back to the correct employee's desk.
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So now all 50 of our backend servers can reach the internet through one public IP address.
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So they remain hidden and protected, no direct access to them from internet, but they can still get what they want from outside.
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At this point, we've built a solid networking foundation, but maintaining all these physical servers is becoming expensive and slow.
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We're spending too much time managing hardware now.
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We have to predict capacity month in advance.
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We have to buy servers, install them, maintain them.
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When we need more capacity, it just takes weeks to set them up.
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So we decided to move TravelBuddy to cloud.
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The cloud means we're renting computing resources instead of owning them.
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So someone else manages the hardware and we can increase or decrease capacity in minutes now instead of weeks.
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But here is an important part.
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The networking concepts we learned do not change.
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We still need IP addresses.
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We still have ports on servers.
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We still have subnets, routing, firewalls, and NAT.
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The cloud just provides these as managed services.
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So in the cloud, we create what's called a virtual private cloud or VPC.
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And this is our own isolated section of the cloud providers network.
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Think of it like renting an office floor in a large office building.
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Other companies are on different floors, but your area is yours.
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Nobody can enter your office, even though they're in the same building.
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Inside our VPC, we create subnets just like before.
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We still have public subnets for things that need internet access and private subnets for things that should be protected.
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We use an internet gateway to connect our public subnets to the internet.
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It's basically like a main entrance to our building.
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We have route tables, which are like signposts
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that tell the data where to go in our network
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and each subnet has a route table
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that directs traffic for private subnets we use net gateway remember
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net from earlier it's the same concept just managed by the
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cloud provider we place a net gateway in a public subnet
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and configure the private subnets to route their outbound internet traffic through it
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so now we have the same secure network architecture we built before
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but running in the cloud with all the benefits of cloud flexibility
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but our application is about to change again
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but before we move on i want to give a huge shout out to polumi for making this video possible
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so you just saw all the infrastructure we built in the cloud the vpc the subnets, the security groups and so on.
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But here's a question.
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How do you actually define and manage all of this infrastructure as code?
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This is where Pulumi really helps because unlike other infrastructure as code tools that use their own domain specific languages,
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Pulumi lets you use the programming languages that you already know like TypeScript, Python, Go, Java, whatever, that you're already using in your tech stack.
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This means you can use your favorite IDE to write infrastructure code with all the features like error checking,
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autocomplete, refactoring, debugging tools that you're already comfortable with.
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And you can write real programming logic instead of being limited by the configuration syntax.
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And here's what's really cool.
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Pulumi just launched Pulumi Neo, which is their new agentic AI built specifically for infrastructure.
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Neo understands your entire infrastructure setup, respects your policies, and it can handle complex tasks end-to-end.
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So you can describe what you need in natural language, and Neo will generate the code,
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review your pull requests, and even help you debug deployments with full understanding of your organization's infrastructure.
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Palomi is open source, so you can use it for free.
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But if you want the enterprise features, you can use my code,
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NANA500, and you're going to get $500 worth of credits to test out those enterprise features.
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I will leave the link in the description.
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Now let's continue with the video.
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As travel buddy grows, our application becomes more complex.
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So we have more services, more dependencies, more things to install and configure.
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And we also move to microservices architecture to make our application or scalable.
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And managing our deployments is actually becoming more and more complex.
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And we're increasingly running into it works on my development laptop, but not on the production server issues.
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And this is where containers solve our problem.
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A container packages everything an application needs, the code, the runtime, all the libraries and settings into one portable package.
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So think of it like the difference between a food truck and a restaurant.
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With a food truck, everything is already inside.
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Just drive it somewhere and start cooking and serving your food.
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Whereas restaurant, you have to find a place
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and you have to set everything up and it's really difficult to move location
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because you have everything tied up in that one restaurant.
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So we use Docker to containerize all of the travel buddies services.
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And now we can run the same container on a developer's laptop, on our test servers, in production, and it works almost identically every time.
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But containers introduce new networking concepts that you need to understand.
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When you run containers on a server, they need to talk to each other.
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Docker creates something called a bridge network, a private network that exists only on that server.
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connected to the same bridge network can actually communicate with each other using just the container names, but containers have their own private networking inside them.
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When our payment service container runs, it might listen on port 1990, for example, inside the container.
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So the question is how do external requests then reach that application running inside the container on port 1990?
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Well, we need to map the containers internal port to a port on the host server.
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So docker run command has a parameter that lets you bind
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or map the port inside container to your host or server's port number.
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So this tells docker take all the traffic
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that arrives on this host server on port 1990 and forward it to port 1990 inside the container called payment.
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Notice this is similar to the net concept that we learned earlier.
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We're translating addresses and ports to bridge between two different networks.
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Now, as we grow even more and we run containers on multiple servers now, because one server is not enough to run all our containers,
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before all our microservices, we need them to communicate with each other across servers, not just on a single server.
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So Docker's overlay network creates a virtual network that spans multiple hosts,
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making containers on different servers appear as if they were on the same network.
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So now with Docker, we've made our application portable and consistent.
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But now we're facing a new challenge, which is managing hundreds of containers, which is absolutely quickly achieved when you have microservices application
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that is running in multiple replicas or copies of the same service for scalability and performance.
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And our travel buddy is successful, so we're running hundreds of containers across dozens of servers.
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And managing this manually is becoming impossible.
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Like which server should a new container run on?
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What happens when a container crashes?
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How do you troubleshoot when something goes wrong when you have hundreds of containers?
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How do you even know that a container crashed
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when you have hundreds of them how do containers find each other
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when they keep moving around from one server to another
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and this is where kubernetes comes into the picture
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so kubernetes automates container management think of it like an automated building manager
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that assigns apartments ensures everything is running and handles maintenance in kubernetes the basic unit is a pod.
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A pod is a group of one or more containers that work closely together.
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Usually it's just one container per pod and each pod gets its own IP address.
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So think of a pod like an apartment unit.
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The apartment has one address and everyone living in that apartment shares that address.
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So all the containers inside a pod will share that same IP address.
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But here's the problem pods are temporary kubernetes can create a
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pod destroy it move it around create a new one at any time
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when you do an update maybe a pod crashed maybe you were updating a version of the application
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and each time kubernetes creates a new pod
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that pod gets a new ip address so
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if our website pod is trying to connect to our database pod
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and the database pod gets recreated with the new ip address
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the website pods connection breaks and pods are ephemeral
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so we shouldn't rely on them being around for a long time
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so how do we solve this problem well this is where
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kubernetes services help us a kubernetes service provides a stable ip address
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and dns name that never changes even as pods behind it come
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and go so we create a service for each of our pods like our database pods
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and service gets a permanent IP address and a DNS name like database service.
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So now when our website pod needs to connect to the database, it connects to database service instead of connecting to a pod directly.
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And the service automatically forwards the connection to one of the healthy active database pods.
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If a database pod dies in the background and gets replaced with a new one, the service automatically updates.
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And the website pod does not notice anything.
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It's still connecting to the same database service.
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It doesn't know what even happened in the background.
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So think of it like a department phone number at a company.
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You call the sales department number and it rings at someone's desk.
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The person might change, but the department number stays the same and there will always be someone who will answer the phone.
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And this is crucial in Kubernetes because pods are constantly being created and destroyed and services provide the stability that we need.
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Now we need to expose our application to the internet.
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We have multiple services running inside our cluster.
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So we need to think how do external users actually reach our applications running inside the cluster?
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Well, we use something called Ingress.
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So Kubernetes Ingress is like a reception desk that routes visitors to the right department based on what they're asking for.
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So a single Ingress can handle all incoming traffic into the cluster
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and route it to the correct service inside the cluster based on the rules that we configure.
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For example, we can say all the requests coming to travelbuddy.com go to website service.
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All the requests coming to travelbuddy.com slash API slash booking go to the booking service.
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Slash API slash payment request to that URL go to the payment service.
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So let's recap what we learned by following Travel Buddy's journey.
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We learned five basic foundational concepts of networking.
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First of all, every device needs a unique identifier, which is an IP address, so others can find it and talk to it.
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And DNS then translates human-friendly names to these IP addresses.
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Second, multiple applications on the same server need different doors to listen on so that traffic goes to the right application.
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So that's the concept of ports.
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We need network segmentation where we divide networks into separate sections
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or subnets for security and organization and routing then connects these sections.
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We also need security in order to control what traffic is allowed between different network segments and to different ports.
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So we need firewall concept for that.
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And finally, when we secure our backend applications within private networks, We need them to still reach the internet directly.
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So NET acts as a gateway, translating their private addresses to a shared public IP address to allow communication to the internet.
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So these five concepts are the foundation of networking and whether you are working with physical servers, cloud infrastructure, Docker containers, or Kubernetes pods,
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these principles actually remain the same.
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So the tools change we went from physical routers to vpcs from physical firewalls to security groups
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but the concepts never change so if you master these fundamentals
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and you'll understand those basic networking concepts then you will understand any networked system
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and you'll be able to troubleshoot optimize applications at any scale now
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if this was helpful then share it with one friend
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or colleague that you know will benefit from this video thank you for watching and I'll see you in the next one.
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このレッスンの語彙とスピーキングのポイント
このB2レベルのスピーキングレッスンは、動画「Every Networking Concept Explained In 20 Minutes」を教材にしています。 繰り返し出てくる語は次のとおりです：server, container, port, pod, application。 この動画には、シャドーイング用の文が275文、単語が3500語あります。 音声の長さは23:20です。 話す速さは1分あたり約150語で、日常会話に近い自然なペースです。 英語の頻出3,000語に含まれる単語は80%だけなので、語彙は難しめです。
この動画の重要語彙
動画の中で特に難しい単語15語を、発音と意味つきで紹介します。
| 単語 | 発音 | 意味 |
|---|---|---|
| container 名詞 | /kənˈteɪ.nəɹ/ | 容器 |
| firewall 名詞 | /ˈfaɪ(ə)ɹˌwɔl/ | 防火壁 |
| pod 名詞 | /ˈpɑd/ | さや |
| translate 動詞 | /tɹænzˈleɪt/ | 訳す, 翻訳する |
| configure 動詞 | /kənˈfɪɡə(ɹ)/ | 設定する |
| divide 動詞 | /dɪˈvaɪd/ | 分割する, 分ける |
| automate 動詞 | /ˈɔ.təˌmeɪt/ | 自動化する |
| memorize 動詞 | /ˈmɛm.əˌɹaɪ̯z/ | 記憶する, 覚える |
| receptionist 名詞 | /ɹɪˈsɛp.ʃə.nɪst/ | 受付係 |
| router 名詞 | /ˈɹaʊ.tɚ/ | ルータ, ルーター |
| segmentation 名詞 | セグメンテーション | |
| install 動詞 | /ɪnˈstɔl/ | 導入する, インストールする |
| checkpoint 名詞 | /ˈt͡ʃɛkˌpɔɪnt/ | チェックポイント, 検問所 |
| compute 動詞 | /kəmˈpjuːt/ | 計算する |
| ephemeral 形容詞 | /ɛˈfɛ.mə.ɹəl/ | はかない, 束の間の |
動画に出てくる句動詞
| 単語 | 発音 | 意味 |
|---|---|---|
| come back 動詞 | 戻る, 帰る | |
| look up 動詞 | /ˌlʊk ˈʌp/ | 見上げる |
繰り返し練習したい文
動画に出てくる短く完結した文です。日常会話でそのまま使えます。
- How do customers actually find our server on the internet?
- We're spending too much time managing hardware now.
- It's basically like a main entrance to our building.
この動画の文法
話し手がよく使っている文型を、動画の実際の表現とともに紹介します。
| 文型 | 動画での表現 |
|---|---|
| 受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる | is called · are numbered · is divided |
| 関係詞節 who / which + 節 — 人や物について情報を加える | servers, which are · tables, which are · Neo, which is |
| 現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している | We've separated · We've created · have now created |
注意したい発音
話し手はwe're, we've, you'llなど、短縮形や弱形を28回使っています。聞こえたとおりの短い形で発音しましょう。
- 「sh」と「zh」の音: receptionist /ɹɪˈsɛp.ʃə.nɪst/, troubleshoot /ˈtɹʌbl̩ˌʃuːt/, foundational /faʊnˈdeɪ.ʃə.nəl/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/, shout /ʃaʊt/
- 長い単語（アクセントの位置に注意）: receptionist /ɹɪˈsɛp.ʃə.nɪst/, ephemeral /ɛˈfɛ.mə.ɹəl/, foundational /faʊnˈdeɪ.ʃə.nəl/, identically /aɪˈdɛntɪkəli/, dependency /dɪˈpɛndənsi/
日本語話者が苦手な音：
- /r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: firewall /ˈfaɪ(ə)ɹˌwɔl/, translate /tɹænzˈleɪt/, troubleshoot /ˈtɹʌbl̩ˌʃuːt/, portable /ˈpɔɹtəbəl/, ephemeral /ɛˈfɛ.mə.ɹəl/
- /v/ — /b/ にならないように、上の歯を下唇に当てる: divide /dɪˈvaɪd/, provider /pɹəˈvaɪ.də(ɹ)/, overlay /ˌoʊvɚˈleɪ/, evolve /ɪˈvɑlv/, visitor /ˈvɪzɪtɚ/
- /f/ — 「フ」ではなく、上の歯と下唇で出す: firewall /ˈfaɪ(ə)ɹˌwɔl/, configure /kənˈfɪɡə(ɹ)/, ephemeral /ɛˈfɛ.mə.ɹəl/, foundational /faʊnˈdeɪ.ʃə.nəl/, configuration /kənˌfɪɡ.əˈɹeɪ̯.ʃən/
この動画での練習方法
- まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
- まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
- 自分の声を録音して元の音声と比べます。container, firewall, podなどの単語に特に注意しましょう。
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。