Elixir/Erlang Applications with Docker in production?

Question

I would like to know what are the strong reasons to go or not to go with the Docker with Elixir/Erlang Application in Production.This is the first time I am asked for starting with the Docker in production.I worked on the production without Docker.I am an Erlang/Elixir Developer.I worked on the high traffic productions servers with millions of transactions per second which are running without Docker.I spent one day for creating and running a Elixir Application image with lots of issues with the network.I had to do lots of configurations for DNS setup etc.After that I started thinking What are the strong reasons for proceeding further.Are there any strong reasons to go or not to go with the Docker with Elixir/Erlang Applications in production.

I went through some of the reasons in the forums but still It am not convinced.All the advantages that docker is providing is already there in the Erlang VM. Could any Erlang Expert in the form please help me.

Answer 1

I deploy Elixir packaged in Docker on AWS in production. This used to be my preferred way of doing things but now I am more inclined to create my own AMI using Packer with everything preinstalled.

The matter central in deployments is that of control, which to a certain extent I feel is relinquished when leveraging Docker.

The main disadvantage of Docker is that it limits the capabilities of Erlang/Elixir, such as internode connection over epmd . This also means that remsh is practically out of the question and the cool :observer.start is a no-no. If you ever need to interact with a production node for whatever reason, there is an extra barrier of entry of first ssh-ing into the server, going inside Docker etc.. Fine when it is just about checking something, frustrating when production is burning down in agony. Launching multiple containers in one Node is kinda useless as the BEAM makes efficient use of all your cores. Hot upgrades are practically out of the question, but that is not really a feature we personally have an intrinsic business need for.

Effort has been made to have epmd working within container setup, such as: https://github.com/Random-Liu/Erlang-In-Docker but that will require you to rebuild Erlang for custom net_kernel modifications.

Amazon has recently released a new feature to AWS ECS, AWS VPC Networking Mode, which perhaps may facilitate inter-container epmd communication and thus connecting to your node directly. I haven't validated that as yet.

Besides the issue of epmd communication is the matter of deployment time. Creating your image with Docker, even though you have images that boast 5MB only, quickly will end up taking 300MB, with 200MB of that just for all the various dependencies to have your release created. There may be ways to reduce that, but that requires specialized knowledge and dedicated effort. I would classify this extra space more as an annoyance as opposed to a deal breaker, but believe me if you have to wait 25 minutes for your immutable deployments to complete, any minute you can shave off would be worthwhile.

Performance wise, I did not notice a significant difference between bare metal deployments and docker deployments. AWS EB Docker nicely expands the container resources to that of the EC2-instance.

The advantage of course is that of portability. If you have a front end engineer that needs to hit a JSON API then in terms of local development it is a huge win that with some careful setup they can just spawn up the latest api running on their local without having to know about Erlang/Elixir/Rserve/Postgres.

Also, Vendor lock-in is greatly reduced, especially ever since AWS launched their support for Kubernetes

This is a question of tradeoffs, if you are a developer who needs to get to production and have very little Devops knowledge, then perhaps a Docker deployment may be warranted. If you are more familiar with infrastructure, deployments etc., then as developer I believe that creating your own AMI gives you more control over your environment. All by all, I would encourage to at least play around with Docker and experiment with it, it may open a new realm of possibilities.

Answer 2

Maybe it depends on the server you want to use. From what I know, for example, Docker facilitates the deployment of a Phoenix application on AWS Elastic Beanstalk a lot, but I'm not competent enough to give you very specific reasons at the moment.

Maybe someone can elaborate more.

Answer 3

Docker is primarily a deployment and distribution tool. From the Docker docs:

Docker streamlines the development lifecycle by allowing developers to work in standardized environments using local containers which provide your applications and services. Containers are great for continuous integration and continuous development (CI/CD) workflows.

If your application has external dependencies (for example, a crypto library), interacts with another application written in another language (for example, a database running as a separate process), or if it relies on certain operating system / environment configuration (you mentioned you had to do some DNS configuration), then packaging your application in a docker container helps you avoid doing duplicate work installing dependencies and configuring the environment. It helps you avoid extra work keeping in sync your testing and production environment in terms of dependencies or investigating why an application works on one machine in one environement, but not another.

The above is not specific to an Erlang application, though I can agree that Erlang helps eliminate some of the problems being cross-platform and abstracting away some of the dependencies, and OTP release handling helps you package your application.

Since you mentioned you are a developer, it is worth mentioning that Docker offers more advantages for an administrator or a team running the infrastructure rather than it does for a developer.