Rewrite scaleDown to fix a series of bugs (#864)

On scaleDown:

- [FIX] Guaranteed stop the runners from the oldest to the newest,
avoiding having runners for too long;
- [FIX] Fixed bug where a runner could be removed from GHA but kept
running on AWS;
- [IMPROVED] Try to maintain always a minimum of `minAvailableRunners`
runners free;

Author: jeanschmidt

terraform-aws-github-runner/modules/runners/lambdas/runners/src/lambda.test.ts

@@ -3,7 +3,7 @@ import { scaleDown as scaleDownL, scaleUp as scaleUpL } from './lambda';
 import { Context, SQSEvent, ScheduledEvent } from 'aws-lambda';
 import { mocked } from 'ts-jest/utils';
 import nock from 'nock';
-import scaleDown from './scale-runners/scale-down';
+import { scaleDown } from './scale-runners/scale-down';
 import { scaleUp } from './scale-runners/scale-up';
 
 jest.mock('./scale-runners/scale-down');

terraform-aws-github-runner/modules/runners/lambdas/runners/src/lambda.ts

@@ -1,6 +1,6 @@
 import { Context, SQSEvent, ScheduledEvent } from 'aws-lambda';
 
-import scaleDownR from './scale-runners/scale-down';
+import { scaleDown as scaleDownR } from './scale-runners/scale-down';
 import { scaleUp as scaleUpR } from './scale-runners/scale-up';
 
 // eslint-disable-next-line @typescript-eslint/no-explicit-any

terraform-aws-github-runner/modules/runners/lambdas/runners/src/scale-runners/gh-runners.ts

@@ -348,7 +348,7 @@ export async function getRunnerTypes(
 
     const config = YAML.parse(configYml);
     const result: Map<string, RunnerType> = new Map(
-      /* eslint-disable @typescript-eslint/no-explicit-any */
+      /* eslint-disable-next-line @typescript-eslint/no-explicit-any */
       (Object.entries(config.runner_types) as [string, any][]).map(([prop, runner_type]) => [
         prop,
         {

terraform-aws-github-runner/modules/runners/lambdas/runners/src/scale-runners/metrics.ts

@@ -578,6 +578,11 @@ export class ScaleDownMetrics extends Metrics {
     this.countEntry('run.count');
   }
 
+  /* istanbul ignore next */
+  exception() {
+    this.countEntry('run.exceptions_count');
+  }
+
   /* istanbul ignore next */
   runnerLessMinimumTime(ec2Runner: RunnerInfo) {
     this.countEntry(`run.ec2runners.notMinTime`);