AWS EB should create new instance once my docker reached its maximum memory limit - scala

Question

I have deployed my dockerized micro services in AWS server using Elastic Beanstalk which is written using Akka-HTTP(https://github.com/theiterators/akka-http-microservice) and Scala.
I have allocated 512mb memory size for each docker and performance problems. I have noticed that the CPU usage increased when server getting more number of requests(like 20%, 23%, 45%...) & depends on load, then it automatically came down to the normal state (0.88%). But Memory usage keeps on increasing for every request and it failed to release unused memory even after CPU usage came to the normal stage and it reached 100% and docker killed by itself and restarted again.
I have also enabled auto scaling feature in EB to handle a huge number of requests. So it created another duplicate instance only after CPU usage of the running instance is reached its maximum.
How can I setup auto-scaling to create another instance once memory usage is reached its maximum limit(i.e 500mb out of 512mb)?
Please provide us a solution/way to resolve these problems as soon as possible as it is a very critical problem for us?

Answer 1

CloudWatch doesn't natively report memory statistics. But there are some scripts that Amazon provides (usually just referred to as the "CloudWatch Monitoring Scripts for Linux) that will get the statistics into CloudWatch so you can use those metrics to build a scaling policy.
The Elastic Beanstalk documentation provides some information on installing the scripts on the Linux platform at http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/customize-containers-cw.html.
However, this will come with another caveat in that you cannot use the native Docker deployment JSON as it won't pick up the .ebextensions folder (see Where to put ebextensions config in AWS Elastic Beanstalk Docker deploy with dockerrun source bundle?). The solution here would be to create a zip of your application that includes the JSON file and .ebextensions folder and use that as the deployment artifact.
There is also one thing I am unclear on and that is if these metrics will be available to choose from under the Configuration -> Scaling section of the application. You may need to create another .ebextensions config file to set the custom metric such as:
option_settings:
aws:elasticbeanstalk:customoption:
BreachDuration: 3
LowerBreachScaleIncrement: -1
MeasureName: MemoryUtilization
Period: 60
Statistic: Average
Threshold: 90
UpperBreachScaleIncrement: 2
Now, even if this works, if the application will not lower its memory usage after scaling and load goes down then the scaling policy would just continue to trigger and reach max instances eventually.
I'd first see if you can get some garbage collection statistics for the JVM and maybe tune the JVM to do garbage collection more often to help bring memory down faster after application load goes down.