Add comment for startupPeriodSeconds

Signed-off-by: Andre Kurait <[email protected]>

deployment/cdk/opensearch-service-migration/lib/service-stacks/migration-service-core.ts

@@ -150,6 +150,13 @@ export class MigrationServiceCore extends Stack {
 
         if (props.maxUptime) {
             let maxUptimeSeconds = Math.max(props.maxUptime.toSeconds(), Duration.minutes(5).toSeconds());
+
+            // This sets the minimum time that a task should be running before considering it healthy.
+            // This is needed because we don't have health checks configured for our service containers.
+            // We can reduce it lower than 30 seconds, and possibly remove it, but then we increase the delay
+            // between the current task being shutdown and the new task being ready to take work. This means
+            // health checks for this container will fail initially and startPeriod will stop ECS from treating
+            // failing health checks as unhealthy during this period.
             let startupPeriodSeconds = 30;
             // Add a separate container to monitor and fail healthcheck after a given maxUptime
             const maxUptimeContainer = serviceTaskDef.addContainer("MaxUptimeContainer", {