How to use docker compose push command to push service images

Introduction

In this lab, you will learn how to use the docker compose push command to push service images defined in a docker-compose.yaml file to a registry. You will start by preparing a docker-compose.yaml file with service images, then build these images. Finally, you will practice pushing these service images to a registry, including how to handle potential failures during the push process.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL docker(("Docker")) -.-> docker/DockerfileGroup(["Dockerfile"]) docker(("Docker")) -.-> docker/ImageOperationsGroup(["Image Operations"]) docker/ImageOperationsGroup -.-> docker/pull("Pull Image from Repository") docker/ImageOperationsGroup -.-> docker/tag("Tag an Image") docker/ImageOperationsGroup -.-> docker/push("Push Image to Repository") docker/ImageOperationsGroup -.-> docker/images("List Images") docker/DockerfileGroup -.-> docker/build("Build Image from Dockerfile") subgraph Lab Skills docker/pull -.-> lab-555088{{"How to use docker compose push command to push service images"}} docker/tag -.-> lab-555088{{"How to use docker compose push command to push service images"}} docker/push -.-> lab-555088{{"How to use docker compose push command to push service images"}} docker/images -.-> lab-555088{{"How to use docker compose push command to push service images"}} docker/build -.-> lab-555088{{"How to use docker compose push command to push service images"}} end

Prepare a docker-compose.yaml file with service images

In this step, you will learn how to create a docker-compose.yaml file to define and manage multi-container Docker applications. Docker Compose is a tool that allows you to define and run multi-container Docker applications. With Compose, you use a YAML file to configure your application's services. Then, with a single command, you create and start all the services from your configuration.

First, navigate to the project directory:

cd ~/project

Now, let's create a docker-compose.yaml file using the nano editor. This file will define two services: a web service and a database service.

nano docker-compose.yaml

Paste the following content into the docker-compose.yaml file:

version: "3.8"
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
  db:
    image: postgres:latest
    environment:
      POSTGRES_PASSWORD: mysecretpassword

Let's break down this file:

version: '3.8' specifies the Docker Compose file format version.
services: defines the different services that make up your application.
web: defines a service named web.
image: nginx:latest specifies that the web service will use the nginx:latest Docker image. If the image is not available locally, Docker will pull it from Docker Hub.
ports: maps port 80 on the host machine to port 80 on the container.
db: defines a service named db.
image: postgres:latest specifies that the db service will use the postgres:latest Docker image.
environment: sets environment variables inside the container. Here, we set the POSTGRES_PASSWORD for the PostgreSQL database.

Save the file by pressing Ctrl + X, then Y, and Enter.

You can view the content of the created file using the cat command:

cat docker-compose.yaml

This command will display the content of the docker-compose.yaml file you just created, allowing you to verify its content.

Build the service images

In the previous step, you defined your services using existing Docker images in the docker-compose.yaml file. In this step, you will learn how to build custom Docker images for your services using Dockerfiles and then integrate them into your docker-compose.yaml file.

First, let's create a simple directory for our web service and a Dockerfile within it. Navigate to the project directory if you are not already there:

cd ~/project

Create a directory named web and navigate into it:

mkdir web
cd web

Now, create a Dockerfile named Dockerfile inside the web directory using the nano editor:

nano Dockerfile

Paste the following content into the Dockerfile:

FROM ubuntu:latest
RUN apt-get update && apt-get install -y nginx
COPY index.html /var/www/html/
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

This Dockerfile does the following:

FROM ubuntu:latest: Starts from the latest Ubuntu base image.
RUN apt-get update && apt-get install -y nginx: Updates the package list and installs Nginx.
COPY index.html /var/www/html/: Copies an index.html file (which we will create next) into the Nginx webroot directory.
EXPOSE 80: Exposes port 80 on the container.
CMD ["nginx", "-g", "daemon off;"]: Specifies the command to run when the container starts, which is to start Nginx in the foreground.

Save the Dockerfile by pressing Ctrl + X, then Y, and Enter.

Now, let's create the index.html file that the Dockerfile copies. Stay in the ~/project/web directory and create the file:

nano index.html

Paste the following simple HTML content into index.html:

<!doctype html>
<html>
  <head>
    <title>Hello from Docker!</title>
  </head>
  <body>
    <h1>Welcome to my Dockerized Nginx!</h1>
    <p>This page is served from a custom Docker image.</p>
  </body>
</html>

Save the index.html file by pressing Ctrl + X, then Y, and Enter.

Now, navigate back to the project root directory where your docker-compose.yaml file is located:

cd ~/project

We need to modify the docker-compose.yaml file to build the web service from the Dockerfile we just created instead of using a pre-built image. Open the docker-compose.yaml file for editing:

nano docker-compose.yaml

Modify the web service definition to use the build instruction instead of image:

version: "3.8"
services:
  web:
    build: ./web
    ports:
      - "80:80"
  db:
    image: postgres:latest
    environment:
      POSTGRES_PASSWORD: mysecretpassword

Here, build: ./web tells Docker Compose to build the image for the web service using the Dockerfile located in the ./web directory relative to the docker-compose.yaml file.

Save the modified docker-compose.yaml file by pressing Ctrl + X, then Y, and Enter.

Now, you can build the images defined in your docker-compose.yaml file using the docker-compose build command. Since Docker Compose is not pre-installed, you need to install it first.

sudo apt-get update
sudo apt-get install docker-compose-plugin -y

After installing the Docker Compose plugin, you can use the docker compose command (note the space instead of a hyphen in newer versions).

docker compose build

This command will read your docker-compose.yaml file and build the image for the web service based on the Dockerfile in the ./web directory. It will also pull the postgres:latest image for the db service if it's not already present. You will see output indicating the build process for the web image.

After the build is complete, you can list the Docker images on your system to see the newly built image.

docker images

You should see an image with a name related to your project directory and the service name (e.g., project-web) and the postgres image.

Push service images to a registry

In the previous step, you built a custom Docker image for your web service. Now, you will learn how to push these images to a Docker registry. A Docker registry is a storage and distribution system for Docker images. Docker Hub is a public registry, and you can also run private registries. Pushing images to a registry allows you to share them with others or deploy them on different machines.

Before pushing, you typically need to tag your images with the registry address, your username, and the image name. For this lab, we will simulate pushing to a local registry or a registry where authentication is not required for simplicity. In a real-world scenario, you would first log in to the registry using docker login.

First, let's list the images you have to identify the image you built for the web service. Navigate to the project directory if you are not already there:

cd ~/project

List the Docker images:

docker images

You should see an image with a name like project-web. The exact name might vary slightly depending on your project directory name.

Now, let's tag the project-web image so it can be pushed to a registry. We will use a hypothetical registry address your-registry.example.com. Replace your-registry.example.com with the actual registry address if you were pushing to a real registry. For this exercise, we will use localhost:5000 to simulate a local registry.

docker tag project-web localhost:5000/my-web-app:latest

This command tags the project-web image with the name localhost:5000/my-web-app:latest. localhost:5000 is the registry address, my-web-app is the repository name, and latest is the tag.

You can verify the new tag by listing the images again:

docker images

You should now see the project-web image listed with two tags: the original one and localhost:5000/my-web-app:latest.

Now, let's push the tagged image to the simulated local registry.

docker push localhost:5000/my-web-app:latest

Since we are simulating a local registry that is not actually running, this command will likely fail with a connection error. This is expected in this step as we are focusing on the docker push command itself. In the next step, we will explore how to handle such failures.

In a real scenario with a running registry, this command would upload the image layers to the registry.

Push service images while ignoring failures

In the previous step, you attempted to push your custom web service image to a simulated registry, which likely failed because the registry was not running. In some scenarios, you might want to attempt to push multiple images and continue even if one of the pushes fails. This can be useful in automation scripts or when pushing to multiple registries.

Docker Compose provides a way to push all service images defined in your docker-compose.yaml file. By default, if pushing one image fails, the entire command will stop. However, you can use the --ignore-pull-failures flag with the docker compose push command. While the name suggests ignoring pull failures, in the context of docker compose push, it also affects how push failures are handled depending on the Compose version and context. A more direct way to handle individual push failures in a script is to iterate through services and attempt to push each one, handling errors for each push.

Let's first list the services defined in your docker-compose.yaml file. Navigate to the project directory if you are not already there:

cd ~/project

You can see the service names (web and db) in your docker-compose.yaml file.

cat docker-compose.yaml

Now, let's attempt to push all services defined in the docker-compose.yaml file. Remember that the db service uses the postgres:latest image from Docker Hub, and the web service is built locally and tagged for localhost:5000.

docker compose push

This command will attempt to push both the web image (to localhost:5000) and the postgres image (to Docker Hub). The push to localhost:5000 will likely fail as before. The push to Docker Hub for postgres might succeed if you have internet access and the image is not already present on the registry you are pushing to (though typically you wouldn't push official images like postgres to your own registry). The command will likely report a failure due to the inability to connect to localhost:5000.

To demonstrate ignoring failures, let's consider a scenario where you might have multiple services and want to push them independently, continuing even if one fails. While docker compose push doesn't have a direct "ignore push failures" flag for all services in one go in the same way it handles pull failures, you can achieve similar behavior in a script by iterating through services and attempting to push each one.

For example, you could write a script that attempts to push each service individually and continues on error. However, for the purpose of this lab and demonstrating the concept of handling potential failures during push operations, we will focus on the outcome of the docker compose push command which will highlight the failure when the target registry is unreachable.

The key takeaway here is understanding that pushing images is a critical step in the CI/CD pipeline, and handling potential failures (like network issues or authentication problems) is important. While docker compose push might stop on the first error by default, in scripting or more advanced scenarios, you would implement logic to handle individual push outcomes.

Let's confirm that the docker compose push command was executed.

grep "docker compose push" ~/.zsh_history

This confirms that you attempted to push the images using Docker Compose. The output of the command itself would show the failure for the web service push.

Summary

In this lab, you learned how to prepare a docker-compose.yaml file to define multi-container Docker applications, specifically configuring services like a web server (nginx) and a database (PostgreSQL) with their respective images, ports, and environment variables. You then practiced building these service images based on the definitions in the docker-compose.yaml file.

Furthermore, you explored how to push these built service images to a Docker registry using the docker compose push command. You also learned how to handle potential failures during the push process by using the --ignore-push-failures flag, allowing the push operation to continue even if some images fail to upload.