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Cloud Spot Instances

Running Playwright E2E tests on CI Spot Instances and using Currents Orchestration to automatically rerouting tests before an eviction.

An additional benefit of using Currents for balancing tests is the ability to automatically redrive tests from one machine to another.

Cost Efficiency of Spot Instances

Many cloud providers have an option to use Spot Instances for running workloads. Using Spot Instances can cost up to 90% lower, compared to the traditionally allocated resources.

Cost optimization with Spot Instances. Source: https://aws.amazon.com/blogs/containers/cost-optimization-for-kubernetes-on-aws/

However, spot instances can be terminated at any time, which can cause the loss of the test results.

Currents Orchestration can automatically reassign the tests from to-be-terminated instance to another machine. This way, the execution can continue without manual intervention.

How it works

Imagine a scenario when you have two machines running a testing suite consisting of two spec files.

  • Machine A - running specA

  • Machine B - running specB

When a spot instance is just about to be terminated (let's say Machine A), Currents will identify the affected spec files and reassign them a different machine.

Reassigning tests in case of spot instance termination

Setup and Configuration

Only tests orchestrated with pwc-p can be dynamically reassigned. Read more about Orchestration Setup.

Starting from version 1.3.0 of @currents/playwright set --pwc-reset-signal CLI parameter:

pwc-p .... --pwc-reset-signal SIGUSR1|SIGUSR2

When specified, pwc-p starts listening to POSIX signal (SIGUSR1 or SIGUSR2). After receiving the signal, it send a request to Currents servers to reassign the affected tests to healthy machines. Currents updates the run status accordingly.

An example output you're expected to see upon termination:

$ npx pwc-p --key XXX --project-id YYY --ci-build-id reset-001 --pwc-reset-signal SIGUSR1

🚥 Will reset tests on SIGUSR1. PID: 66640
🚀 Starting orchestration session...
📦 Currents reporter: 1.3.0 recording CI build reset-001 for project YYY
🎭 Playwright: 1.44.0 1 test in 1 project [chromium] 

🌐 Executing orchestrated task: [chromium] test.spec.ts 
🌐 Run URL: https://app.currents.dev/run/c11610c6e1644913

================================================================

2024-05-15T23:31:57.336Z starting test attempt #1: [chromium] › test.spec.ts:15:5 › A

# in another terminal: kill -SIGUSR1 66640

🚥 Received SIGUSR1
🚥 Resetting tests: machineId: 3SN5zz9Mhl2ALzzB, runId: c11610c6e1644913
🚥 Success resetting tests: machineId: 3SN5zz9Mhl2ALzzB, runId: c11610c6e1644913

It is your responsibility to capture the eviction notice, detect the PID and send the signal to pwc-p process before an eviction.

  • usr1 normally activates the Node.js debugger, but this ability is disabled when we listen on usr1

  • usr2 normally treated as a exit in Node.js, so if you pass it WITHOUT turning on our listener, you will immediately kill the process

  • You must send the signal to pwc-p process - not the npx or wrapper process. The parent process will behave as noted above and not pass the signal down to our process.

Refer to the following documentation for capturing the eviction notice for various cloud providers:

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