Deploying a Haskell Server to AWS

In the last few articles, we've been talking about how to deploy a Haskell application using AWS. This is part 3 of the series. So if you haven't done parts 1 & 2, you should start there so you can follow along!

In Part 1, we wrote a Dockerfile and created a local Docker image containing a simple program for a Haskell web server.

In the Part 2, we pushed our container image to the AWS container registry (ECR). Notably, this involved creating an AWS account, downloading AWS command line tools and authenticating on the command line. We'll run a couple more of these commands today, so hopefully you're still authenticated!

But now that our container is uploaded, deploying that container is fairly straightforward. But it requires us to use a couple new concepts, as we'll see.

Adding ECR Permission

Before we get started, there's one step we have to take on the web portal. You need to give Elastic Beanstalk permission to download your ECR containers. You can do this using the IAM service from the AWS portal. Then follow these steps:

1. Select "roles" on the left hand menu.
2. Select "aws-elasticbeanstalk-ec2-role" in the list in the middle of the screen.
3. Click "Add Permissions"
4. Search for and select "AmazonEC2ContainerRegistryReadOnly"

Now let's get into the steps on our local machine.

Configuration File

There are multiple approaches to deploying a docker container, but the one that worked most easily for me was to create a file called Dockerrun.aws.json. (Full other methods, refer to the documentation). This approach involves a counter-intuitive idea. We're going to create a separate directory outside of our main project directory. We'll call it remote.

~/Quiz $ cd ..
~/ $ mkdir remote && cd remote

In this directory, we'll make a single file, called Dockerrun.aws.json. This will, of course, be a JSON file. It will be a very simple configuration file telling our application to use the docker image we pushed last time to ECR. We have to start it by specifying the version of the program (which is 1 because we're only using a single container).

{
  "AWSEBDockerrunVersion": "1",
  ...
}

Now we'll use tell it to use the Docker image we pushed last time by giving the URI under the Image object:

{
  "AWSEBDockerrunVersion": "1",
  "Image": {
    "Name": "165102442442.dkr.ecr.us-west-2.amazonaws.com/quiz-server"
  },
  ...
}

Finally, we'll specify the port, similar to a Dockerfile. We'll use 8080 both for the "Container" port and the "Host" port.

{
  "AWSEBDockerrunVersion": "1",
  "Image": {
    "Name": "165102442442.dkr.ecr.us-west-2.amazonaws.com/quiz-server"
  },
  "Ports": [{
    "ContainerPort": 8080,
    "HostPort": 8080
  }]
}

This is the only file we need in this directory! So now let's see what commands we need to run.

Creating the Application

Now we have two more steps that can largely be accomplished on the command line. First, we have to create an application. Then we have to create an environment to use for that application.

Before we can create an application though, we have to create a Git repository, just to store our single file! That's how AWS figures out what to push for configuration.

~/remote $ git init
~/remote $ git add .
~/remote $ git commit -m "First Commit"

Now we can create the application using the eb init command. We'll give our application the name quiz-server.

~/remote $ eb init -p docker quiz-server

You can then see your application on the web portal by accessing the "Elastic Beanstalk" service and clicking the "Applications" tab on the left menu.

Creating the Environment

Now we have to deploy an environment to deploy for our application. When first creating this environment, we use the eb create command. We'll give this environment the name quiz-server-env.

~/remote $ eb create quiz-server-env

This will take a while to deploy. But once it's done, you should be able to see it by clicking the "Environments" tab from the previous screen in the web portal. This will also show you the URL you can use to access your server. It's now successfully deployed!

Debugging

Sometimes, your deployment might fail. For example, you might misspell the name of your container. If you click on your environment (from the "Environments" tab), then you'll be able to access the "Logs" on the left hand menu. This can help you debug. If you need to change your configuration file, you'll need to commit it, though you don't need to push it to any remote repository. You instead use eb deploy to push your changes.

~/remote $ git add Dockerrun.aws.json
~/remote $ git commit -m "New Commit"
~/remote $ eb deploy

Now the deployment process should start again!

Video

You can also watch our YouTube video to see all these steps in action!

Conclusion

You now have enough information to deploy a Haskell web application to Heroku! We'll have one more installment in this series around adding a database to our application, so stay tuned for that! In the meantime, subscribe to our monthly newsletter so you can stay up to date with all the latest news!