docker
/
docs
mirror of https://github.com/docker/docs.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

ENGDOCS-2001 (#19580) 

* ENGDOCS-2001

* SG fixes

* tech review

* minor edit

* Apply suggestions from code review

Co-authored-by: Craig Osterhout <103533812+craig-osterhout@users.noreply.github.com>

---------

Co-authored-by: Craig Osterhout <103533812+craig-osterhout@users.noreply.github.com>
This commit is contained in:
Allie Sadler 2024-03-21 07:16:41 +00:00 committed by GitHub
parent 24e6d280de
commit 6e130b1a56
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 139 additions and 141 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

280
content/compose/gettingstarted.md
View File

@ -8,20 +8,22 @@ keywords: docker compose example, docker compose tutorial, how to use docker com
title: Try Docker Compose
---
This tutorial is designed to introduce the key concepts of Docker Compose whilst building a simple Python web application. The application uses the Flask framework and maintains a hit counter in
Redis.
This tutorial aims to introduce fundamental concepts of Docker Compose by guiding you through the development of a basic Python web application.
Using the Flask framework, the application features a hit counter in Redis, providing a practical example of how Docker Compose can be applied in web development scenarios.
The concepts demonstrated here should be understandable even if you're not familiar with Python.
This is a non-normative example that just highlights the key things you can do with Compose.
## Prerequisites
You need to have Docker Engine and Docker Compose on your machine. You can either:
- Install [Docker Engine](../get-docker.md) and [Docker Compose](install/index.md) as standalone binaries
- Install [Docker Desktop](../desktop/index.md) which includes both Docker Engine and Docker Compose
Make sure you have:
You don't need to install Python or Redis, as both are provided by Docker images.
- Installed the latest version of Docker Compose
- A basic understanding of Docker concepts and how Docker works
## Step 1: Define the application dependencies
## Step 1: Set up
1. Create a directory for the project:
@ -59,12 +61,12 @@ You don't need to install Python or Redis, as both are provided by Docker images
```
In this example, `redis` is the hostname of the redis container on the
application's network. We use the default port for Redis, `6379`.
application's network and the default port, `6379` is used.
> Handling transient errors
> **Note**
>
> Note the way the `get_hit_count` function is written. This basic retry
> loop lets us attempt our request multiple times if the redis service is
> loop attempts the request multiple times if the Redis service is
> not available. This is useful at startup while the application comes
> online, but also makes the application more resilient if the Redis
> service needs to be restarted anytime during the app's lifetime. In a
@ -79,50 +81,47 @@ You don't need to install Python or Redis, as both are provided by Docker images
redis
```
## Step 2: Create a Dockerfile
4. Create a `Dockerfile` and paste the following code in:
The Dockerfile is used to build a Docker image. The image
contains all the dependencies the Python application requires, including Python
itself.
```dockerfile
# syntax=docker/dockerfile:1
FROM python:3.10-alpine
WORKDIR /code
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run", "--debug"]
```
In your project directory, create a file named `Dockerfile` and paste the following code in:
{{< accordion title="Understand the Dockerfile" >}}
```dockerfile
# syntax=docker/dockerfile:1
FROM python:3.10-alpine
WORKDIR /code
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run"]
```
This tells Docker to:
This tells Docker to:
* Build an image starting with the Python 3.10 image.
* Set the working directory to `/code`.
* Set environment variables used by the `flask` command.
* Install gcc and other dependencies
* Copy `requirements.txt` and install the Python dependencies.
* Add metadata to the image to describe that the container is listening on port 5000
* Copy the current directory `.` in the project to the workdir `.` in the image.
* Set the default command for the container to `flask run --debug`.
* Build an image starting with the Python 3.10 image.
* Set the working directory to `/code`.
* Set environment variables used by the `flask` command.
* Install gcc and other dependencies
* Copy `requirements.txt` and install the Python dependencies.
* Add metadata to the image to describe that the container is listening on port 5000
* Copy the current directory `.` in the project to the workdir `.` in the image.
* Set the default command for the container to `flask run`.
{{< /accordion >}}
>Important
>
>Check that the `Dockerfile` has no file extension like `.txt`. Some editors may append this file extension automatically which results in an error when you run the application.
{ .important }
> **Important**
>
>Check that the `Dockerfile` has no file extension like `.txt`. Some editors may append this file extension automatically which results in an error when you run the application.
{ .important }
For more information on how to write Dockerfiles, see the
[Docker user guide](../develop/index.md)
and the [Dockerfile reference](/reference/dockerfile/).
For more information on how to write Dockerfiles, see the [Docker user guide](../develop/index.md) and the [Dockerfile reference](/reference/dockerfile/).
## Step 2: Define services in a Compose file
## Step 3: Define services in a Compose file
Compose simplifies the control of your entire application stack, making it easy to manage services, networks, and volumes in a single, comprehensible YAML configuration file.
Create a file called `compose.yaml` in your project directory and paste
the following:
@ -145,7 +144,11 @@ It then binds the container and the host machine to the exposed port, `8000`. Th
The `redis` service uses a public [Redis](https://registry.hub.docker.com/_/redis/)
image pulled from the Docker Hub registry.
## Step 4: Build and run your app with Compose
For more information on the `compose.yaml` file, see [How Compose works](compose-application-model.md).
## Step 3: Build and run your app with Compose
With a single command, you create and start all the services from your configuration file.
1. From your project directory, start up your application by running `docker compose up`.
@ -175,13 +178,13 @@ image pulled from the Docker Hub registry.
Compose pulls a Redis image, builds an image for your code, and starts the
services you defined. In this case, the code is statically copied into the image at build time.
2. Enter http://localhost:8000/ in a browser to see the application running.
2. Enter `http://localhost:8000/` in a browser to see the application running.
If this doesn't resolve, you can also try http://127.0.0.1:8000.
If this doesn't resolve, you can also try `http://127.0.0.1:8000`.
You should see a message in your browser saying:
```console
```text
Hello World! I have been seen 1 times.
```
@ -191,7 +194,7 @@ image pulled from the Docker Hub registry.
The number should increment.
```console
```text
Hello World! I have been seen 2 times.
```
@ -214,12 +217,11 @@ image pulled from the Docker Hub registry.
5. Stop the application, either by running `docker compose down`
from within your project directory in the second terminal, or by
hitting CTRL+C in the original terminal where you started the app.
hitting `CTRL+C` in the original terminal where you started the app.
## Step 5: Edit the Compose file to add a bind mount
## Step 4: Edit the Compose file to use Compose Watch
Edit the `compose.yaml` file in your project directory to add a
[bind mount](../storage/bind-mounts.md) for the `web` service:
Edit the `compose.yaml` file in your project directory to use `watch` so you can preview your running Compose services which are automatically updated as you edit and save your code:
```yaml
services:
@ -227,128 +229,124 @@ services:
build: .
ports:
- "8000:5000"
volumes:
- .:/code
environment:
FLASK_DEBUG: "true"
develop:
watch:
- action: sync
path: .
target: /code
redis:
image: "redis:alpine"
```
The new `volumes` key mounts the project directory (current directory) on the
host to `/code` inside the container, allowing you to modify the code on the
fly, without having to rebuild the image. The `environment` key sets the
`FLASK_DEBUG` environment variable, which tells `flask run` to run in development
mode and reload the code on change. This mode should only be used in development.
Whenever a file is changed, Compose syncs the file to the corresponding location under `/code` inside the container. Once copied, the bundler updates the running application without a restart.
## Step 6: Re-build and run the app with Compose
For more information on how Compose Watch works, see [Use Compose Watch](file-watch.md). Alternatively, see [Manage data in containers](../storage/volumes.md) for other options.
From your project directory, type `docker compose up` to build the app with the updated Compose file, and run it.
> **Note**
>
> For this example to work, the `--debug` option is added to the `Dockerfile`. The `--debug` option in Flask enables automatic code reload, making it possible to work on the backend API without the need to restart or rebuild the container.
> After changing the `.py` file, subsequent API calls will use the new code, but the browser UI will not automatically refresh in this small example. Most frontend development servers include native live reload support that works with Compose.
## Step 5: Re-build and run the app with Compose
From your project directory, type `docker compose watch` or `docker compose up --watch` to build and launch the app and start the file watch mode.
```console
$ docker compose up
Creating network "composetest_default" with the default driver
Creating composetest_web_1 ...
Creating composetest_redis_1 ...
Creating composetest_web_1
Creating composetest_redis_1 ... done
Attaching to composetest_web_1, composetest_redis_1
web_1 | * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
$ docker compose watch
[+] Running 2/2
✔ Container docs-redis-1 Created 0.0s
✔ Container docs-web-1 Recreated 0.1s
Attaching to redis-1, web-1
⦿ watch enabled
...
```
Check the `Hello World` message in a web browser again, and refresh to see the
count increment.
> Shared folders, volumes, and bind mounts
>
> * If your project is outside of the `Users` directory (`cd ~`), then you
need to share the drive or location of the Dockerfile and volume you are using.
If you get runtime errors indicating an application file is not found, a volume
mount is denied, or a service cannot start, try enabling file or drive sharing.
Volume mounting requires shared drives for projects that live outside of
`C:\Users` (Windows) or `/Users` (Mac), and is required for _any_ project on
Docker Desktop for Mac and Docker Desktop for Windows that uses
[Linux containers](../desktop/faqs/windowsfaqs.md#how-do-i-switch-between-windows-and-linux-containers).
For more information, see
[File sharing on Docker for Mac](../desktop/settings/mac.md#file-sharing),
[File sharing on Docker for Windows](../desktop/settings/windows.md#file-sharing), [File sharing on Docker for Linux](../desktop/settings/linux.md#file-sharing).
and the general examples on how to
> [Manage data in containers](../storage/volumes.md).
>
> * If you are using Oracle VirtualBox on an older Windows OS, you might encounter an issue with shared folders as described in this [VB trouble
ticket](https://www.virtualbox.org/ticket/14920). Newer Windows systems meet the
requirements for [Docker Desktop for Windows](../desktop/install/windows-install.md) and do not
need VirtualBox.
{ .important }
## Step 6: Update the application
## Step 7: Update the application
To see Compose Watch in action:
As the application code is now mounted into the container using a volume,
you can make changes to its code and see the changes instantly, without having
to rebuild the image.
Change the greeting in `app.py` and save it. For example, change the `Hello World!`
1. Change the greeting in `app.py` and save it. For example, change the `Hello World!`
message to `Hello from Docker!`:
```python
return 'Hello from Docker! I have been seen {} times.\n'.format(count)
```
```python
return 'Hello from Docker! I have been seen {} times.\n'.format(count)
```
Refresh the app in your browser. The greeting should be updated, and the
2. Refresh the app in your browser. The greeting should be updated, and the
counter should still be incrementing.
![hello world in browser](images/quick-hello-world-3.png)
![hello world in browser](images/quick-hello-world-3.png)
3. Once you're done, run `docker compose down`.
## Step 7: Split up your services
Using multiple Compose files lets you customize a Compose application for different environments or workflows. This is useful for large applications that may use dozens of containers, with ownership distributed across multiple teams.
1. In your project folder, create a new Compose file called `infra.yaml`.
2. Cut the Redis service from your `compose.yaml` file and paste it into your new `infra.yaml` file. Make sure you add the `services` top-level attribute at the top of your file. Your `infra.yaml` file should now look like this:
```yaml
services:
redis:
image: "redis:alpine"
```
3. In your `compose.yaml` file, add the `include` top-level attribute along with the path to the `infra.yaml` file.
```yaml
include:
- infra.yaml
services:
web:
build: .
ports:
- "8000:5000"
develop:
watch:
- action: sync
path: .
target: /code
```
4. Run `docker compose up` to build the app with the updated Compose files, and run it. You should see the `Hello world` message in your browser.
This is a simplified example, but it demonstrates the basic principle of `include` and how it can make it easier to modularize complex applications into sub-Compose files. For more information on `include` and working with multiple Compose files, see [Working with multiple Compose files](multiple-compose-files/_index.md).
## Step 8: Experiment with some other commands
If you want to run your services in the background, you can pass the `-d` flag
(for "detached" mode) to `docker compose up` and use `docker compose ps` to
see what is currently running:
- If you want to run your services in the background, you can pass the `-d` flag (for "detached" mode) to `docker compose up` and use `docker compose ps` to see what is currently running:
```console
$ docker compose up -d
```console
$ docker compose up -d
Starting composetest_redis_1...
Starting composetest_web_1...
Starting composetest_redis_1...
Starting composetest_web_1...
$ docker compose ps
$ docker compose ps
Name Command State Ports
-------------------------------------------------------------------------------------
composetest_redis_1 docker-entrypoint.sh redis ... Up 6379/tcp
composetest_web_1 flask run Up 0.0.0.0:8000->5000/tcp
```
Name Command State Ports
-------------------------------------------------------------------------------------
composetest_redis_1 docker-entrypoint.sh redis ... Up 6379/tcp
composetest_web_1 flask run Up 0.0.0.0:8000->5000/tcp
```
The `docker compose run` command allows you to run one-off commands for your
services. For example, to see what environment variables are available to the
`web` service:
- Run `docker compose --help` to see other available commands.
```console
$ docker compose run web env
```
- If you started Compose with `docker compose up -d`, stop your services once you've finished with them:
See `docker compose --help` to see other available commands.
```console
$ docker compose stop
```
If you started Compose with `docker compose up -d`, stop
your services once you've finished with them:
```console
$ docker compose stop
```
You can bring everything down, removing the containers entirely, with the `down`
command. Pass `--volumes` to also remove the data volume used by the Redis
container:
```console
$ docker compose down --volumes
```
- You can bring everything down, removing the containers entirely, with the `docker compose down` command.
## Where to go next
- Try the [Sample apps with Compose](https://github.com/docker/awesome-compose)
- [Explore the full list of Compose commands](reference/index.md)
- [Explore the Compose file reference](compose-file/index.md)
- To learn more about volumes and bind mounts, see [Manage data in Docker](../storage/index.md)