Triggering an Amazon ECS from Amazon RDS

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With a few lines of code, it’s possible to trigger an Amazon Elastic Container Service (ECS) from an Amazon Relational Database Service (RDS). This article intends to describe how to do it and the struggles I had while trying to have it working.

For the sake of understanding, I will describe an imaginary system to explain why I want to trigger an ECS task. Let’s pretend user data protection just doesn’t exist.

The company IT Paradise offers a cafeteria to its employees where they can order coffee, snacks, and drinks. Since they are riding the “healthy style” wave, they decided to follow the employee’s consumption habits.

IT Paradise implemented a system that tracks the amount of coffee and snacks an employee takes a day. So now, every time someone goes to the Cafeteria and swipe their card, the Cafeteria’s system “A” inserts the consumed items on a database table, which triggers a lambda to run an ECS task.

The ECS task starts the application “B” that will process the information about the employee intakes and feed the employee’s profile on a system “C”. When everything is done, system “B” stops itself.

Imaginary system’s flow

The database

The database is an Aurora MySQL and it will need the permissions as described on AWS documentation.

We create a trigger on the table that holds the purchases of the employee. Check line 9 for the piece of code that calls the lambda.

Database trigger to call the lambda

The Lambda Saga

Since I’m a Java enthusiast I naively wrote my lambda in Java 11. However, I faced several problems and gave up in a “NoClassDefFoundError” (line 14).

Besides that, my jar ended up with 150mb, which is a lot for what I needed, and the initialization time was also discouraging.

I leave the Java 11 non-working code below just for the records.

When I finally accepted that it was to much trouble to a simple task, I tested a script in Node.js and it worked smoothly and painlessly. :)

It can be checked below. It has plenty of room to improve, but the important thing to note here is that I always get the last version of the task definition (line 27) and the runTask command (line 56).

Lambda working script (Node.js 12.x)

Lambda permissions are as below.

Basic permission that lambda needs to access CloudWatch logs.
Allows the lambda to interact with ECS and run tasks.

Conclusions

As far as I’m aware, it’s not possible to trigger Amazon ECS directly from my Amazon RDS Aurora, thus the need for the lambda.

A lambda can be easily called from the Amazon RDS and then, from the lambda, it is possible to run an Amazon ECS task.

After the tests, I got a little bit disappointed with lambdas in Java on AWS, but it’s incredibly easy to work with lambdas in Node.js.

By taking the approach described, it is possible to have a detached architecture with exclusive containers running only during the necessary amount of time and avoid some “pains” such as schedulers or memory share. Also, it saves money! We don’t have the container always up and running and we will pay only for what we use.

Special thanks to my DevOps Elson Neto that guided me through the AWS permissions maze and my colleague Diego Hordi for suggesting some nice touches.

Software Engineer. Always learning.

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