Run selenium tests at scale using ECS Fargate

This article talks about an approach that can help customers run integration and regression tests quicker and cheaper to improve the CI/CD process.

Introduction

Let us consider a scenario where the developer has added a new feature or made a bug fix to an existing product and checked the changes. As part of the CI/CD pipeline, the new code gets built, unit test cases are run and deployed in a QA or staging environment. Once the deployment is successful QA team will run the integration and regression test cases to certify the build. In a typical case, the number of test cases may vary between hundreds to a few thousand, so executing these test cases will take time, eventually slowing down the phase in which features get deployed in production. The traditional way of accelerating this test case execution is one of the following:

Add more resources to the QA team so they can start these test case execution in parallel from multiple machines, monitor them, and collect results
Add more physical machines or VM's, so we have enough browser agents to run these tests rather than relying on local machines

This method is not scalable and costs both money and time. The approach explained here focuses on this specific problem and walks through how we can run these test cases quicker without costing a lot of money and time.

Note: The approach highlighted here is only applicable for testcases executed using selenium framework

Security

See CONTRIBUTING for more information.

License

This library is licensed under the MIT-0 License. See the LICENSE file.

Architecture

Here is the high-level view of all the components

Notes

Selenium Hub is used to parallelize and distribute the load between the browser agents for test case execution.
The whole infrastructure gets deployed in ECS Cluster with the following strategy for the default capacity provider:
- FARGATE -> Base: 4, Weight: 1
- FARGATE_SPOT -> Weight: 4

Note: Out of 5 instances, 4 of them will get provisioned as SPOT, and one of them will get provisioned as ON_DEMAND

Selenium Hub, "Chrome Node (selenium docker image with headless chrome), and Firefox Node (selenium docker image with headless firefox) are deployed as ECS services
All ECS services have autoscaling enabled, with the following scale in and scale out policies:
- Add three instances if max(CPUUtilization) >= 70 in last 1 minute
- Remove one instance if max(CPUUtilization) <= 30 in last 1 minute
Selenium Hub is backed by an "Application Load Balancer" to which web driver clients connect to run the tests CloudWatch logs enable-Observability.

The code available in this repository is exposed as an CDK Construct, to learn more about CDK Construct click here

Benefits

Here are some key benefits of using this approach:

Depending upon the number of concurrent execution, ChromeNode & FirefoxNode will scale out and in automatically (as it impacts the CPUUtilization metrics), so the customer pay's only for the duration they use (no standing cost)
Customer can deploy different browsers or different versions of the same browser depending upon the business need without thinking about the infrastructure or cost
Based on the capacity provider strategy, most of the instances gets provisioned as FARGATE_SPOT, which costs way less money, so to facilitate quicker execution, scale quicker with more nodes
With this approach, customers can now run the regression and integration test cases part of their nightly builds that would enable daily release cycle to support growing business needs.

Test case execution

Here is the sequence of events that happens when we execute a test case using this architecture

Build & Deploy

Pre-requistes

AWS CDK should be installed in the local laptop. You can read more about it here
Yarn needs to be installed, you can check the installation status by running this command

yarn version

Output 1.22.10

If Yarn is not installed run the following command

npm install -g yarn

An AWS account and console access

Deployment

Check out the code from this repository using this command:

mkdir scaling-test-execution && cd scaling-test-execution
git clone https://github.com/hariohmprasath/scaled-test-execution.git .

As the code is created as a CDK construct, the following parameters can be customized as part of the deployment

Parameter	Description	Default
vpc	VPC in which the resources needs to be created	New VPC will be created
seleniumVersion	Selenium version used in the docker image	3.141.59
memory	Memory settings for hub and chrome fargate nodes	512
cpu	CPU settings for hub and chrome fargate nodes	256
seleniumNodeMaxInstances	Selenium `NODE_MAX_INSTANCES` pointing to the number of instances of the same version of browser that can run in node	5
seleniumNodeMaxSessions	Selenium `NODE_MAX_SESSION` pointing to the number of browsers (Any browser and version) that can run in parallel at a time in node	5
minInstances	Minimum number of instances for autoscaling chrome, firefox and selenium services	1
maxInstances	Maximum number of instances for autoscaling chrome, firefox and selenium services	10

Run the following command to start the deployment

cdk deploy --require-approval never

Once the deployment is successful, you should see the 'Selenium-Hub-DNS' in the CfnOutput.

The complete selenium hub load balancer URL will look like.

http://<<Selenium-Hub-DNS>>:4444/wd/hub

Testing

Unit testing

Unit testcases can be executed by running the following command from the root directory

yarn test

Output

$ npx projen test
🤖 test | rm -fr lib/
🤖 test » test:compile | tsc --noEmit --project tsconfig.jest.json
🤖 test | jest --passWithNoTests --all --updateSnapshot
PASS  test/hello.test.ts
✓ create app (730 ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |       72 |     100 |     100 |
 index.ts |     100 |       72 |     100 |     100 | 61-70
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        5.163 s
Ran all test suites.
🤖 test » eslint | eslint --ext .ts,.tsx --fix --no-error-on-unmatched-pattern src test build-tools .projenrc.js
✨  Done in 17.45s.

Integration testing (using webdriver)

A sample test case can you found under sample-test-function folder, you can run the following commands to build and execute the tests against the selenium hub load balancer url

cd sample-test-function && npm install
npx wdio --hostname <<Selenium-Hub-DNS>>

Output

All test cases should successfully pass and here is how it looks like

[chrome 87.0.4280.88 linux #0-0] Running: chrome (v87.0.4280.88) on linux
[chrome 87.0.4280.88 linux #0-0] Session ID: 80329f4643463a93a4628a35de4aaab4
[chrome 87.0.4280.88 linux #0-0]
[chrome 87.0.4280.88 linux #0-0] Play with google
[chrome 87.0.4280.88 linux #0-0]    ✓ navigate to the site
[chrome 87.0.4280.88 linux #0-0]    ✓ start a search
[chrome 87.0.4280.88 linux #0-0]
[chrome 87.0.4280.88 linux #0-0] 2 passing (8.2s)


Spec Files:	1 passed, 1 total (100% completed) in 00:00:10

Load testing (using webdriver)

Scale up

To simulate load test we ran the above mentioned testcase in parallel (closer to 10 concurrent session), which made the CPUUtilization to go above 70%, resulting in autoscaling.

Here are few screen shots captured using Container Insights and AWS ECS console

AWS ECS Console

ECS Tasks

ECS Service

Graphs using Container Insights

ECS Cluster