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* chore(deps-dev): switch to prettier 3.6.2 Signed-off-by: Jeff MAURY <jmaury@redhat.com>
165 lines
7.8 KiB
Markdown
165 lines
7.8 KiB
Markdown
---
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sidebar_position: 8
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title: Getting started with Compose
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description: Getting started with Compose on Podman Desktop
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keywords: [podman-desktop, compose, containers, containerfile, docker-compose, dockerfile, multi-container]
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tags: [podman-desktop, working-with-compose]
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---
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# Getting started with Compose
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[Compose is a specification](https://www.compose-spec.io/) for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services, networks, and volumes. This allows you to capture in a single file the entire configuration necessary to run a set of interconnected containers as an application. For example, if you have an application that requires a web server, a database, and a caching service, you can define these components and their relationships in your Compose file.
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To use the Compose YAML, you can leverage a specification implementation, such as [`podman compose`](https://docs.podman.io/en/latest/markdown/podman-compose.1.html) and [`docker compose`](https://github.com/docker/compose).
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This tutorial covers the following end-to-end tasks required to use a multi-container Compose application within Podman Desktop:
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- [Download and run the example application](/tutorial/getting-started-with-compose#download-and-run-the-example-application) using `podman compose up`.
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- [View the guestbook web application](/tutorial/getting-started-with-compose#viewing-the-guestbook-application).
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- [View and modify the database](/tutorial/getting-started-with-compose#viewing-and-modifying-the-database) to check the guestbook web application is synchronized and running correctly.
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- [Scale database replicas](/tutorial/getting-started-with-compose#scaling-more-replicas).
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## Before you begin
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If you do not have Compose installed, you can follow the complete onboarding process to install it system wide:
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1. Install the Compose extension from the catalog. For more details, see [Installing a Podman Desktop extension](https://podman-desktop.io/docs/extensions/install).
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1. Set up Compose and complete the onboarding process to configure it system-wide.
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1. Check that you are able to run `podman compose`:
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```sh
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podman compose
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Run compose workloads via an external provider such as docker-compose or podman-compose
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Description:
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This command is a thin wrapper around an external compose provider such as docker-compose or podman-compose. This means that podman compose is executing another tool that implements the compose functionality but sets up the environment in a way to let the compose provider communicate transparently with the local Podman socket. The specified options as well the command and argument are passed directly to the compose provider.
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...
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```
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:::note
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If Compose is already installed, you have the option to upgrade or downgrade its version by navigating to the **Settings > CLI Tools** page.
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:::
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## Download and run the example application
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Our example application is located at [github.com/redhat-developer/podman-desktop-demo](https://github.com/redhat-developer/podman-desktop-demo).
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1. Run `git clone` to build the Go binary web application:
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```sh
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git clone https://github.com/redhat-developer/podman-desktop-demo
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cd podman-desktop-demo/guestbook-compose
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```
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1. Run `podman compose up -d` to start the application:
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```sh
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podman compose up -d
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>>>> Executing external compose provider "/usr/local/bin/docker-compose". Please refer to the documentation for details. <<<<
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[+] Running 3/3
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✔ Container redis-replica Started 0.0s
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✔ Container web Started 0.0s
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✔ Container redis-leader Started 0.0s
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```
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## Viewing the guestbook application
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Within Podman Desktop, you can now see that all three containers are up and operational.
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1. Click the "Open Browser" button to view the web application:
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1. Within the Guestbook web application, you can:
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- "Sign" the guestbook, which will write to the Redis leader and synchronize to the replicas.
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- "Read" from the guestbook, which will read from the pool of Redis replicas. This allows for readability even if the Redis leader is unavailable.
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- `/env`: View the container's environment variables.
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- `/info`: View information about the Redis cluster.
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## Viewing and modifying the database
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Using Podman Desktop, you can also access the container's terminal directly from the GUI and modify the database.
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1. Click **Open Terminal** to access the `redis-leader` terminal:
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1. Modify the database as if you are doing database administration:
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1. Run `redis-cli` within the container to access the Redis database.
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2. Type `LPUSH guestbook "Hello World!"` and you will see your web application update in real-time.
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3. Type `DEL guestbook` and you will see that your database drops the `guestbook` key and clears the database.
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Changes will reflect in real-time on the guestbook.
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You can further modify the database and see the changes propagate to the Redis replicas. For example, view the logs of the `redis-replica`, and you will notice that there are periodic database synchronizations as well as reads to the database:
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### How does it work?
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A quick overview of how the architecture works in this multi-container scenario:
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- Within the Guestbook application, it looks for a database with the names `redis-leader` and `redis-replica` on port `6379`.
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- Because it is a Compose application, the containers are connected on the same network. This means that a neighboring container can be network-accessible simply by its container name.
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There is a set of environment variables that the web application can modify in the Compose application:
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- `REDIS_LEADER`: The default is `redis-leader`.
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- `REDIS_REPLICAS`: The default is `redis-replica`. It can be comma-separated, such as `redis-replica-1,redis-replica-2`.
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- `REDIS_PORT`: The default is `6379`.
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- `SERVER_PORT`: The default is `8080`.
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## Scaling more replicas
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Want to scale more replicas? This can be achieved by adding an environment variable to your `compose.yaml` and duplicating your `redis-replica` entry.
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1. Modify your `compose.yaml` as follows:
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```yaml
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services:
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redis-leader:
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container_name: redis-leader
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image: redis:latest
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ports:
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- '6379'
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redis-replica:
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container_name: redis-replica
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image: redis:latest
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ports:
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- '6379'
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command: redis-server --replicaof redis-leader 6379
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redis-replica-2:
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container_name: redis-replica-2
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image: redis:latest
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ports:
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- '6379'
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command: redis-server --replicaof redis-leader 6379
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web:
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container_name: web
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build: ./web
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ports:
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- '8080:8080'
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```
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1. Run `podman compose up -d` again to ensure the new container has been added and the new environment variable has propagated:
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```sh
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podman compose up -d
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>>>> Executing external compose provider "/usr/local/bin/docker-compose". Please refer to the documentation for details. <<<<
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[+] Running 4/4
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✔ Container redis-replica-2 Started 0.0s
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✔ Container redis-leader Running 0.0s
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✔ Container web Started 0.0s
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✔ Container redis-replica Running 0.0s
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```
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