From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- .../docker/compose%2Fgettingstarted%2Findex.html | 123 +++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 devdocs/docker/compose%2Fgettingstarted%2Findex.html (limited to 'devdocs/docker/compose%2Fgettingstarted%2Findex.html') diff --git a/devdocs/docker/compose%2Fgettingstarted%2Findex.html b/devdocs/docker/compose%2Fgettingstarted%2Findex.html new file mode 100644 index 00000000..75ab44ae --- /dev/null +++ b/devdocs/docker/compose%2Fgettingstarted%2Findex.html @@ -0,0 +1,123 @@ +

Get started with Docker Compose

+ +

On this page you build a simple Python web application running on Docker Compose. The application uses the Flask framework and maintains a hit counter in Redis. While the sample uses Python, the concepts demonstrated here should be understandable even if you’re not familiar with it.

Prerequisites

Make sure you have already installed both Docker Engine and Docker Compose. You don’t need to install Python or Redis, as both are provided by Docker images.

Step 1: Setup

Define the application dependencies.

  1. Create a directory for the project:

    $ mkdir composetest
+$ cd composetest
+

  2. Create a file called app.py in your project directory and paste this in:

    import time
+
+import redis
+from flask import Flask
+
+app = Flask(__name__)
+cache = redis.Redis(host='redis', port=6379)
+
+def get_hit_count():
+    retries = 5
+    while True:
+        try:
+            return cache.incr('hits')
+        except redis.exceptions.ConnectionError as exc:
+            if retries == 0:
+                raise exc
+            retries -= 1
+            time.sleep(0.5)
+
+@app.route('/')
+def hello():
+    count = get_hit_count()
+    return 'Hello World! I have been seen {} times.\n'.format(count)
+

    In this example, redis is the hostname of the redis container on the application’s network. We use the default port for Redis, 6379.

    Handling transient errors

    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 not available. This is useful at startup while the application comes online, but also makes our application more resilient if the Redis service needs to be restarted anytime during the app’s lifetime. In a cluster, this also helps handling momentary connection drops between nodes.

  3. Create another file called requirements.txt in your project directory and paste this in:

    flask
+redis
+

Step 2: Create a Dockerfile

In this step, you write a Dockerfile that builds a Docker image. The image contains all the dependencies the Python application requires, including Python itself.

In your project directory, create a file named Dockerfile and paste the following:

# syntax=docker/dockerfile:1
+FROM python:3.7-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:

For more information on how to write Dockerfiles, see the Docker user guide and the Dockerfile reference.

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and paste the following:

version: "3.9"
+services:
+  web:
+    build: .
+    ports:
+      - "8000:5000"
+  redis:
+    image: "redis:alpine"
+

This Compose file defines two services: web and redis.

Web service

The web service uses an image that’s built from the Dockerfile in the current directory. It then binds the container and the host machine to the exposed port, 8000. This example service uses the default port for the Flask web server, 5000.

Redis service

The redis service uses a public Redis image pulled from the Docker Hub registry.

Step 4: Build and run your app with Compose

  1. From your project directory, start up your application by running docker-compose up.

    $ 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)
+redis_1  | 1:C 17 Aug 22:11:10.480 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
+redis_1  | 1:C 17 Aug 22:11:10.480 # Redis version=4.0.1, bits=64, commit=00000000, modified=0, pid=1, just started
+redis_1  | 1:C 17 Aug 22:11:10.480 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
+web_1    |  * Restarting with stat
+redis_1  | 1:M 17 Aug 22:11:10.483 * Running mode=standalone, port=6379.
+redis_1  | 1:M 17 Aug 22:11:10.483 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
+web_1    |  * Debugger is active!
+redis_1  | 1:M 17 Aug 22:11:10.483 # Server initialized
+redis_1  | 1:M 17 Aug 22:11:10.483 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
+web_1    |  * Debugger PIN: 330-787-903
+redis_1  | 1:M 17 Aug 22:11:10.483 * Ready to accept connections
+

    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.

    If you’re using Docker natively on Linux, Docker Desktop for Mac, or Docker Desktop for Windows, then the web app should now be listening on port 8000 on your Docker daemon host. Point your web browser to http://localhost:8000 to find the Hello World message. If this doesn’t resolve, you can also try http://127.0.0.1:8000.

    You should see a message in your browser saying:

    Hello World! I have been seen 1 times.
+

    hello world in browser

  3. Refresh the page.

    The number should increment.

    Hello World! I have been seen 2 times.
+

    hello world in browser

  4. Switch to another terminal window, and type docker image ls to list local images.

    Listing images at this point should return redis and web.

    $ docker image ls
+
+REPOSITORY        TAG           IMAGE ID      CREATED        SIZE
+composetest_web   latest        e2c21aa48cc1  4 minutes ago  93.8MB
+python            3.4-alpine    84e6077c7ab6  7 days ago     82.5MB
+redis             alpine        9d8fa9aa0e5b  3 weeks ago    27.5MB
+

    You can inspect images with docker inspect <tag or id>.

  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.

Step 5: Edit the Compose file to add a bind mount

Edit docker-compose.yml in your project directory to add a bind mount for the web service:

version: "3.9"
+services:
+  web:
+    build: .
+    ports:
+      - "8000:5000"
+    volumes:
+      - .:/code
+    environment:
+      FLASK_ENV: development
+  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_ENV 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.

Step 6: Re-build and run the app with Compose

From your project directory, type docker-compose up to build the app with the updated Compose file, and run it.

$ 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)
+...
+

Check the Hello World message in a web browser again, and refresh to see the count increment.

Shared folders, volumes, and bind mounts

Step 7: Update the application

Because 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! message to Hello from Docker!:

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 counter should still be incrementing.

hello world in browser

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:

$ docker-compose up -d
+
+Starting composetest_redis_1...
+Starting composetest_web_1...
+
+$ 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
+

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:

$ docker-compose run web env
+

See docker-compose --help to see other available commands.

If you started Compose with docker-compose up -d, stop your services once you’ve finished with them:

$ 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:

$ docker-compose down --volumes
+

At this point, you have seen the basics of how Compose works.

Where to go next

+

documentation, docs, docker, compose, orchestration, containers

+
+

+ © 2019 Docker, Inc.
Licensed under the Apache License, Version 2.0.
Docker and the Docker logo are trademarks or registered trademarks of Docker, Inc. in the United States and/or other countries.
Docker, Inc. and other parties may also have trademark rights in other terms used herein.
+ https://docs.docker.com/compose/gettingstarted/ +

+
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