This lets Docker cache our dependencies into its own layer so that if we ever change our source code later but not our dependencies we dont need to re-run yarn install and wait forever while theyre all installed again. Lets just say we wanted to update the docker-compose.yml file above to change the redis image to their alpine version, and yes you should always use alpine whenever possible! This is why I like to enable an init process in all of my docker containers by using the init command in docker compose like so: Bear in mind init works with version 2.2 of docker-compose and 3.7 onwards as specified in the yaml above. :/app so you can benefit from having code updates without having to rebuild your image(s). Normally you would see the full path being listed out, such as /home/python/.local/bin/gunicorn instead of gunicorn. # The output of `ps` when you use the array (exec) variant: # The output of `ps` when you use the string (shell) variant: # This will clean up old md5 digested files since they are volume persisted. But one general takeaway is to remove unnecessary files and dont forget to ignore all of your .env files because you wouldnt want to copy sensitive files into your image because now if you pushed your image to a Docker registry now that registry has access to your sensitive information since its in your image. Here we can default to false for production but then for our dev environment in our .env file we can set it to true. Ive written a more detailed post on expose vs publish in Docker Tip #59. This is in the Webpack stage of all of my example apps and its very specific to using PostCSS. It was a 29 minute talk where I covered a bunch of Docker Compose and Dockerfile patterns that Ive been using and tweaking for years while developing and deploying web applications. You might think that volume mounted files will be owned by the node:node user and group on your dev box which likely wont exist, so youll end up with errors. Technically Kubernetes will disable a HEALTHCHECK if it finds one in your Dockerfile because it has its own readiness checks but the takeaway here is if we can avoid potential issues then we should. All in all when you combine environment variables with Docker Compose and build args with your Dockerfile you can use the same code in all environments while only changing a few env variables. The basic idea is you could create that file and add something like this to it: Its a standard Docker Compose file, and by default when you run a docker-compose up then Docker Compose will merge both your docker-compose.yml file and docker-compose.override.yml into 1 unit that gets run. Whenever possible I try to make decisions that make my apps able to be hosted on a wide range of services. You can define environment variables in this file by setting something like ${FLASK_ENV}. These should be "development" or "production". Since the worker service isnt running a web server it doesnt make sense to do this copy operation twice so we set an empty entrypoint. # external links outside of your domain then feel free remove this line. The only place this typically doesnt work is on CI servers because you cant control the uid:gid of the CI user. The array version is preferred and even recommended by Docker. Regardless of your tech stack theres a few things youll likely want to configure for your app server. Instead it will be expected you transfer your .env file over to your server and let Docker Compose make it available with the env_file property. Im only going to include relevant lines to what were talking about btw, check out the example apps for a complete Dockerfile reference. However, if you follow the example apps well want to make sure the public/ directory always exists so thats why theres a .keep file. Thats all I tried but it might be necessary with other languages. Its better because the shell variant will not pass Unix signals such as SIGTERM, etc. Although even for single server deploys with any tech stack its useful to know what resources your services require because it can help you pick the correct hardware specs of your server to help eliminate overpaying or under-provisioning your server. As for the .env file, well ignore all of them except for our example file. For example, in the Dockerfile for the Flask example the Python image does not create a user for you. This is nice because it means if you upgrade servers later on you dont need to worry about updating any configuration, not even an env variable. In the above case, in my .yarnrc file Ive customized where Node packages will get installed to by adding --modules-folder /node_modules to that file. This means we have a single source of truth (.env file) for these values and we never have to change the Dockerfile or docker-compose.yml file to change their value. Both options will run gunicorn but theres a pretty big difference between the 2 variants. If you didnt do that step theyll still be owned as root:root. You can see this port when you run docker container ls: Since were publishing a port we can see both the published and exposed port, but if we didnt publish the port in our docker-compose.yml file the PORTS column would be totally empty if we didnt set EXPOSE 8000 in our Dockerfile. But fortunately it doesnt work exactly like that. Speaking of defaults, I try to stick to using what I want the values to be in production. This way when its being overwritten we know exactly whats its being changed to. Hes really good at coming up with great names! This file will have a combination of secrets along with anything that might change between development and production. With gunicorn youll need to explicitly configure gunicorn to do code reloading or not. That means youll end up having multiple .env.X files in your repo, all of which should be ignored. By default it runs the curl command but in our .env file we can set export DOCKER_WEB_HEALTHCHECK_TEST=/bin/true in development. The hello directory in this case is the Flask apps name. The above health check returns a 200 if its successful but it also makes sure the app can connect to PostgreSQL and Redis. Docker-compose is a very useful tool when you need to orchestrate multiple containers, especially if those containers serve a common purpose. Without knowing this information, you may end up wasting resources on your cluster. This way you can use different values in whatever environment needs them, and you can have them both default to 1000. It seems like weve gone full circle back to the days when Docker Compose used to be called Fig and version 1 had no version definition. In development I set both of these values to 1 in the .env.example because its easier to debug an app that doesnt fork under the hood. Here are some tips I use often because I find rather useful. Let us know below. The takeaway here is all of your apps can log to stdout and then you can handle logging at the Docker daemon level in 1 spot. This doesnt bloat anything in the end because only the final assets get copied over in another build stage. # These lines are important but I've commented them out to focus going over the other 3 lines. Its a good idea to log to stdout instead of a file on disk when working with Docker because if you log to disk itll disappear as soon as you stop and remove your container. By the way, I have a new course coming out focused on deploying web apps with Terraform, Ansible and Docker Compose. This is prime pickings for an environment variable. Of course that comes with the downside of not being able to use shell scripting in your CMD such as wanting to use && but thats not a big deal in the end. By default Docker Compose will look for an .env file in the same location as your docker-compose.yml file to find and use that env vars value. This is Docker 101 stuff but the basic idea is to copy in our package management file (package.json file in this case), install our dependencies and then copy in the rest of our files. Overall I try not to make assumptions about where I might deploy my apps to. If for whatever reason your set up is unique and 1000:1000 wont work for you you can get around this by making UID and GID build arguments and pass their values into the useradd command (discussed below). Its also a good idea to set a default value in case its not defined which you can do with ${FLASK_ENV:-production}. If youre running native Linux or are using WSL 2 on Windows, chances are your user account also has 1000:1000 as its uid:gid because that is a standard Unix convention since its the first user account created on the system. For example without setting that, we wouldnt be able to run gunicorn without supplying the full path to where it exists which would be /home/python/.local/bin/gunicorn in our case. # Which environment is running? For example, if its a deterministic task you may want to consider putting it into a RUN instruction in your Dockerfile so it happens at build time (such as installing dependencies). With Python, Ruby and some other languages your worker and thread count control how many requests per second your app server can serve. In development it doesnt matter how many we override because that can all be set up and configured in the example file beforehand. But in practice this doesnt end up being an issue because you can disable the mounts in CI. A majority of the patterns are applied exactly the same with any language and web framework and I just want to quickly mention that Im in the process of putting together example apps for a bunch of languages and frameworks. The Docker Compose spec mentions that the version property is deprecated and its only being defined in the spec for backwards compatibility. Also running commands, even if you script them, doesnt give you the capabilities that docker-compose gives you to inspect the state of whats running and apply changes on the fly and manage container elegantly. Its a very fast running command that returns exit code 0 which will make the health check pass. That means I prefer defining my health check in the docker-compose.yml file instead of a Dockerfile. End to end that entire endpoint will likely respond in less than 1ms with most web frameworks so it wont be a burden on your server. But in development it would be a bit crazy if you rebooted your dev box and every project you ever created in your entire life came up so we can set export DOCKER_RESTART_POLICY=no to prevent them from starting automatically. Shes a software engineer who primarily works with Scala and by sheer luck we ended up getting in contact about something unrelated to Docker. Heres what a health check looks like when defining it in a docker-compose.yml file: Whats neat about this pattern is it allows us to adjust our health check in development vs production since the health check gets set at runtime. If you want to delve deeper into yaml templating capability for docker-compose check out this article. However with that said, going back to file permissions if you did need to customize the UID and GID, using build arguments is a reasonable thing to do. If you ever found yourself not being able to see your servers logs in Docker Compose its because you likely need to set this or the equivalent var in your language of choice. Ive truncated the gunicorn paths so it fits on 1 line. In that case you could automatically generate a .env file with all your required variables that would replaced in your docker-compose.yml file. Youll see both are set to 1 in the example apps that have app servers which support these options. Likewise with Redis, thats a basic connection test. This also works if you happen to use WSL 1 along with Docker Desktop. This isnt the only thing you can use ENTRYPOINT scripts for. Without setting that I was getting a race condition error in the cp command because it was trying to copy files from 2 different sources very quickly because both the web and worker services are sharing that volume. You could log to journald and then explore your logs with journalctl (great for single server deploys) or have your logs get sent to CloudWatch on AWS or any 3rd party service. In the above case NODE_ENV is being set as a build argument, then an env variable is being set with the value of that build arg, and finally production assets are being built in the image only when the NODE_ENV is not development. I chose python because one pattern I detected is that most official images that create a user for you will name the user based on the image name. And in dev you can set export DOCKER_WEB_PORT_FORWARD=8000 in the .env file to allow connections from anywhere. As a disclaimer, these are all personal opinions. All of the example apps come configured with GitHub Actions and solve this problem. So thats about it. Docker Compose 1.26+ is compatible with export. All of concepts well talk about will apply to just about any web framework. Its also worth pointing out that when you set the command property in docker-compose.yml it will automatically convert the string syntax into the array syntax. In all 3 cases Ill be using Docker but how they run is drastically different. If you happen to use TailwindCSS this is really important to set. Dive into Docker takes you from "What is Docker?" Certain packages may expect this to be set, and using . On May 27th, 2021 I gave a live demo for DockerCon 21. If you set 0 then your services will use as many resources as they need which is effectively the same as not defining these properties. If you are dealing with containers and you want to create a network and assign them ips you can do the following: However, you can also use the name of the service as your dns and you will be able to talk to other containers without the need to create a network. Then we can volume mount out those files so nginx can read them. Setting the PATH is a reasonable idea too because if you start running your containers as a non-root user and install your packages in your users home directory or a custom location you wont be able to access binaries directly. In a similar fashion you could also define: REDIS_URL = os.getenv("REDIS_URL", "redis://redis:6379/0"). Now configuring your database is as easy as changing an env variable in your .env file. Some official images create a user for you, others do not. This is necessary to ensure that the directory ends up being owned by the correct user. Also, youll be in much better shape to deploy your app into Kubernetes or other container orchestration platforms. This is only 1 example of how you can make use of multi-stage builds. # Always keep this here as it ensures the built and digested assets get copied. is useful too. As for the Play example, I want to give a huge shout out to Lexie. This will help with creating portable and repeatable Docker images too. Thats handy if youre running Docker in a self managed VM instead of using Docker Desktop or in cases where you want to access your site on multiple devices (laptop, iPad, etc.) Ive created a separate video on that topic. On the topic of development / production parity I like using the same docker-compose.yml in all environments. We are also defining restart:always which will restart the container automatically if it crashes. The idea is to support using POSTGRES_* env variables that match up with what the official PostgreSQL Docker image expects us to set, however the last line is interesting because it lets us pass in a DATABASE_URL which will get used instead of the individual env vars. Thats because if Kubernetes knows your app uses 75mb of memory it knows it can fit 10 copies of it on a server with 1 GB of memory available. A healthy application is a happy application, but seriously having a health check endpoint for your application is a wonderful idea. This mount itself could be read-only or a read-write mount based on whether or not you plan to support uploading files directly to disk in your app. The above is a snippet from the Webpack build stage of the Flask example app. I fully expect discovering new things over time and tweaking my set up as Docker introduces new features and I improve my skills. The chown node:node is important there because without it our custom /node_modules directory wont be writeable as the node user. In the past Ive used /healthy but switched to /up after hearing DHH (the creator of Rails) mention that name once. For developer convenience you can also add a docker-compose.override.yml.example to your repo that isnt ignored from version control and now all you have to do is cp docker-compose.override.yml.example docker-compose.override.yml to use the real override file when cloning down the project. Theres no way that Play example app could have existed without her help and expertise. On fully managed servers or container orchestration platforms typically you wouldnt be using bind mounts so its a non-issue. Thats because the BEAM (Erlang VM) will gobble up as many resources as it can which could interfere with other services you have running, such as your DB and more. That prevents folks on the internet from accessing example.com:8000 without needing to set up a cloud firewall to block whats been set by Docker in your iptables rules. With the dedicated health check in place now you can use it with Docker Compose, Kubernetes or an external monitoring service like Uptime Robot. I went with DATABASE_URL as the name because its a convention that a lot of hosting providers use. In the Node build stage we build our bundled assets into an /app/public directory, but the above line is being used in the Python build stage which copies those files to /public. Instead, if you log to stdout you can configure Docker to persist your logs however you see fit. That means in dev we wont get barraged by log output related to the health check firing every minute. Lets say that you have multiple environments that are mostly the same except for a few different configurations that are different. In the end it means well have smaller images to pull and run in production. You can also override an aliased property in a specific service which lets you customize it. Local development with a local copy of PostgreSQL running in Docker and a managed database of your choosing in production. The above ENTRYPOINT script runs in a few hundred milliseconds and its only necessary because volume mounts arent something you do at build time. If you made it to the end thanks a lot for reading it! With Docker Compose v1.27+ you can drop it all together, yay for deleting code! Lots of app servers default to localhost which is a gotcha when working with Docker because itll block you from being able to connect from your browser on your dev box. Its informative only. Instead /bin/true will run which is pretty much a no-op. from nginx thats not running in a container then a bind mount is a reasonable choice. This pattern isnt limited to yarn too. Basically if you want something to run every time your container starts then using an ENTRYPOINT script is the way to go, but you should think carefully about using one. We only end up with a few CSS, JS and image files. It allows for you to hook up automated tools to visit this endpoint on a set interval and notify you if something abnormal happens, such as not getting an HTTP status code 200 or even notify you if it takes a really long time to get a response. Thats a better option to keep your docker-compose files as simple as possible.
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docker compose best practices