Understanding Docker in Production

Question

I've been learning how to use Docker to setup dev environments, however, I'm curious how these ideas translate to a production stack. As an example, I have a Laravel (Php) app, which uses MySQL, Redis, and Nginx

So in production, let's say I would normally have 2 application ec2 instances behind a load balancer on AWS. When setting up a similar production situation using Docker...

1) because I'd be using RDS and Elasticache, there would be no need for containers for those. So basically, id only need containers for PHP-Fpm and Nginx?

2) to have high availability, I would still have 2 (or least more than 1) ec2 instances behind the ELB. So I suppose each instance would run the above containers (PHP and Nginx). But that sounds no different than my previous VM setup, where each server runs what it needs to serve the application. Is that accurate?

3) with VMs, I would traditionally bake the code into an AMI and add those AMIs to a Launch Configuration and an Auto Scaling group, and that group would spin up instances as needed. So for deployment, I would tear down the old ec2 instances and spin up new ones. With Docker, Since these containers would be running on ec2 instances, wouldn't i still have to spin up / tear down the VMs, or would I just replace the containers and keep the VMs running?

Answer 1

Its reasonable to keep RDS, Elasticache and other fully managed services, outside of docker environment. Yes for high availability you need multiple EC2 instances having docker daemon running.

The real advantage is not coming with having two EC2 instances running two web server docker containers on each of them. Real advantages comes when you break down your application to microservices, where multiple containers in combination construct your web application providing the benefits of microservices.

Apart from that the DevOps flow would be different compared to traditional web application deployment in EC2 with autoscaling and load balancing and have many benefits. For example your source code will contain the container code as well, which will guarantee, the environment will work uniformly in your staging and production. Also you will be having images pointing to branches/tags in your source control, which allows to get new updates(delta downloads) for new releases.

If you are going to setup docker in AWS, its recommended to go with AWS ECS to reduce management overhead.

Answer 2

1. You're right, you will only need to run your code in a container and it will simply access the remote services. The only thing you'll have to consider is to ensure connectivity to them.

2. You're right again, you'll need to have everything you previously had in your VMs in the Docker container so that your code works as before. Anyway, with Docker containers it is possible to run multiple instances of your app on the same EC2 instance. Of course, your app will try to run on the same port, so some extra networking layer is needed for managing ports is necessary, but it's possible. All the EC2 instances needs to have is docker installed.

3. Instead of creating AMIs and closing and spinning up EC2 instances, you'll only have to pull the new Docker image and restart the container with the new image. This means just a few seconds compared to minutes in the EC2 instances flow. This is means you have a really quick way of reverting buggy deploys and opens the doors for a setup in which 0% downtime can be reached.