Deploy Multiple services to Elastic Beanstalk - example with Static Files & Python Flask - amazon-web-services

Question

Background
Elastic beanstalk can be configured to serve multiple different processes through the application load balancer configuration.
In this example, let's assume we're configuring a static file server alongside a flask api endpoint.
The below picture, shows that we can create two processes, one api, pointing to port 2000 and the default process passing through at port 80.
Adding the rules in the ALB, means that we can have the incoming listener route to specific processes based on the path prefix. In this example, anything that starts with /api/* is being forwarded on to the api application while the remaining traffic falls through to the default service.
Question
This is all well and good, we now have an elastic beanstalk environment that can host multiple services. However, what's not clear is how does one actually go about deploying to target a specific process?
In a single process scenario, you just type eb deploy on a directory that's had eb init applied to it and off you go. Now, how does one go about deploying multiple processes using eb deploy and specifically how can one target the 'api' process or the 'default' process with their deployment in this example?

Answer 1

The question remains for how to get a deployment to target processes, but there is
an option for how to get this working specifically with static files that does not involve tweaking the ALB as per the question.
Create a folder in your root called .ebextensions
Within that, create a file anything.config - let's call it python.config and add the code below
option_settings:
aws:elasticbeanstalk:environment:proxy:staticfiles:
/html: html
The syntax of /html: html maps the incoming url path to a path on your local path that you eb deploy from (same level as .ebextensions) - In this case, the url path /html is the same as the physical folder name on the server, but that need not be the case.
Important: Do not add a trailing slash e.g./html/: html/ will not work
Nginx configs behind the scenes
By default, elastic beanstalk uses NGinx, a proxy server, that allows you to configure how to map url prefixes to locations on the drive.
By creating the above setting in .ebextensions, a new config value is created for the nginx server that sits in front of your application inside the ec2 instance that runs your app.
You can see this in action yourself, by logging on to your instance and navigating to the nginx staging area config below:
/var/proxy/staging/nginx/conf.d/elasticbeanstalk/
Where you will see the following files:
00_application.conf 01_static.conf healthd.conf
This setting is responsible for creating the 01_static.conf file with the following contents, aliasing any html request to the folder of the same name deployed under /var/app/current/
location /html {
alias /var/app/current/html;
access_log off;
}
To rapidly test nginx configuration changes without requiring eb deploy cycles, you can tweak the config from the final location located at
/etc/nginx/conf.d/elasticbeanstalk/01_static.conf
And then do a
service nginx restart
That's how I discovered, that the trailing slash was causing issues in my case.