Networking 2 Containers

Resources

• Getting Started with Docker and AI by Nigel Poulton

• Docker Cheatsheet

• Docker Hub Container Image Library | App Containerization

Sam

Problem: We move to microservices for scalability, but deployment becomes harder. Solution: A container packages everything an application needs into 1 portable unit.

• code

• runtime

• libraries

• settings

Glossary

Figure 1.12 Diagram

Sam

Images: a read-only template containing everything needed to run a container

Container: a running, isolated instance of an image

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Registry: a centralized place for storing and retrieving images

Host: where (physical server or VM) the container executes. The host provides the OS that every container shares.

Runtime environment: where the program executes + the necessary resources/services

Kernel: the core features & functions of an OS. (Sometimes kernel & OS are used interchangeably.)

Microservices: a design pattern where every feature is dev/deployed/managed as its own small app/microservice

Bridge network: a private network that exists only on that server and allows containers to talk.

Images & Containers

Sam

Issue: dev & prod environments had different versions of libraries & dependencies.

Solution: Docker makes it easy to package applications + dependencies.

• image: the standard package

• container: the standard runtime

Containers virtualize the OS, not the hardware.

Sam

The steps in containerizing an application:

1. Dev app

2. Package app + dependencies as an image (called containerization)

3. Ship image to a registry (optional)

4. Run as a container (using a tool like Docker)

A container is a ring-fenced part of an OS dedicated to a single app. (isolated execution environment)

Sam

Under the hood:

Shared OS (kernel)

• Container 1 (runs 1 app)

• Container 2 (runs 1 app)

• Container ...

Each container is NOT aware of others.

Images

3 layers ⟶ 1 image

Containers

1 image ⟶ 1+ containers

Registries

Sam

registries

• are: centralized places to store & retrieve images

• aka: container registries | Docker registries | OCI registries.

actions (Figure)

• pushing: storing images

• pulling: retrieving images

Microservices

Sam

• Old way: monolithic applications. Every feature is dev/deployed/managed as 1 complex app.

• New way: microservices. Every feature is dev/deployed/managed as its own indy app.

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The term microservice comes from:

• Small (micro)

• Application (service)

microservices: a design pattern where indy app features are dev/deployed/managed as indy apps running as containers.

Sam

Example: 1 microservices application with 6 microservices.

Each of the 6 microservices:

• is built as its own image

• is deployed as its own container

• is coupled with other microservices over the IP network.

• can be updated & scaled independently

Docker Compose

Sam

Docker Compose is how we can deploy/manage multi-container apps (aka microservices apps).

Note that Compose refers to containers as services.

The compose file is where we define the app.

• define the services

• define the network

Deploy using docker compose command.

Example:Figure 6.2. The Compose file.