runners: Add expiration policy to SSM parameters (#6885)

This adds an expiration policy to the SSM parameters for the runners.
This is to ensure that the parameters are deleted after 30 minutes.

Github Runner Tokens typically have a 1 hour expiration time, but our
runners are typically expected to be up way quicker than that so 30
minutes is a good balance for when we expect the runners to be up.

If a runner isn't conencted to Github by at least 30 minutes we will
more than likely have spun it down and it will be deleted.

This is an attempted re-land of 2 commits:
* #6855
* #6858

---------

Signed-off-by: Eli Uriegas <eliuriegas@meta.com>

Author: seemethere

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

@@ -1263,7 +1263,27 @@ describe('createRunner', () => {
         Name: 'wg113-i-1234',
         Value: 'us-east-1-BLAH',
         Type: 'SecureString',
+        Policies: expect.any(String),
       });
+      // Verify the Policies parameter contains the correct expiration policy structure
+      const putParameterCall = mockSSM.putParameter.mock.calls[0][0];
+      const policies = JSON.parse(putParameterCall.Policies);
+      expect(policies).toEqual([
+        {
+          Type: 'Expiration',
+          Version: '1.0',
+          Attributes: {
+            Timestamp: expect.any(String),
+          },
+        },
+      ]);
+
+      // Verify the timestamp is approximately 30 minutes in the future
+      const expirationTime = new Date(policies[0].Attributes.Timestamp);
+      const now = Date.now();
+      const timeDiff = expirationTime.getTime() - now;
+      expect(timeDiff).toBeGreaterThan(25 * 60 * 1000); // at least 25 minutes (allowing for test execution time)
+      expect(timeDiff).toBeLessThan(35 * 60 * 1000); // at most 35 minutes (allowing for clock differences)
     });
 
     it('creates ssm experiment parameters when joining experiment', async () => {
@@ -1307,6 +1327,7 @@ describe('createRunner', () => {
         Name: 'wg113-i-1234',
         Value: 'us-east-1-BLAH #ON_AMI_EXPERIMENT',
         Type: 'SecureString',
+        Policies: expect.any(String),
       });
       expect(mockEC2.runInstances).toBeCalledTimes(1);
       expect(mockEC2.runInstances).toBeCalledWith(

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

@@ -392,6 +392,18 @@ async function addSSMParameterRunnerConfig(
                 Name: parameterName,
                 Value: runnerConfig,
                 Type: 'SecureString',
+                // NOTE: This does need to be an stringified JSON array of objects, check docs at:
+                // https://docs.aws.amazon.com/systems-manager/latest/userguide/example_ssm_PutParameter_section.html
+                Policies: JSON.stringify([
+                  {
+                    Type: 'Expiration',
+                    Version: '1.0',
+                    Attributes: {
+                      //  Expire after 30 minutes from present time
+                      Timestamp: new Date(Date.now() + 1000 * 60 * 30).toISOString(),
+                    },
+                  },
+                ]),
               })
               .promise();
             return parameterName;