AEM Workflow Debugging — 6.5 LTS / AMS

Production-grade debugging for AEM Granite Workflow engine, launcher, Inbox, Sling Jobs, thread pools, and purge on AEM 6.5 LTS and Adobe Managed Services (AMS).

Variant Scope

• This skill is 6.5-lts-only (includes AMS).
• Full JMX access via Felix Console or JMX client.
• Config changes via Felix Console or OSGi config in repository.

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When to use this skill

• Workflow stuck, not progressing, failed, not starting, task not in Inbox, purge/repository bloat, permissions, queue backlog, thread pool exhaustion, auto-advancement not working.
• User provides thread dumps, configuration status ZIPs, Sling Job console output, or error.log excerpts.
• Environment: AEM 6.5 LTS / AMS (JMX available).

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Step 1: Map symptom to first action

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Step 2: Decision tree (workflow stuck)

1. No current work item? → Stale. JMX: countStaleWorkflows → restartStaleWorkflows(dryRun=true).
2. Participant step → Assignee exists? Inbox visible? Payload accessible? Dynamic participant resolver returning correct user?
3. Process step → Search error.log for instance ID. Check: process.label registered, payload path exists, bundle active, no exception in execute().
4. OR/AND Split → Condition evaluates correctly? Routes exist? No dead-end branches? Model synced?

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Step 3: Thread dump & thread pool analysis

Thread dumps on 6.5 / AMS are obtained via jstack or by requesting from AMS support. Configuration status ZIPs from Felix Console → Status → Configuration Status.

3a. Sling default thread pool (critical path)

The Sling Scheduler ApacheSlingdefault uses ThreadPool: default. This pool runs:

• Oak observation events
• All Quartz-scheduled jobs — including the workflow timeout-detection scheduler that emits com/adobe/granite/workflow/timeout/job events to the Sling Job system (the job itself then runs on the Granite Workflow Queue, see Step 3c)

Check the Sling Thread Pools status page (/system/console/status-slingthreadpools):

If active count = max pool size AND block policy = ABORT:

• New scheduled tasks (including workflow timeout/auto-advance jobs) are silently rejected
• This is the #1 cause of auto-advancement failure

Check the Threads status page (/system/console/status-Threads) or the jstack thread dump (/system/console/status-jstack-threaddump):

• Search for sling-default- threads
• If all threads show same stack (e.g. stuck on HTTP call, database, or external service), that's the blocking culprit
• Note elapsed time — threads stuck for hours indicate a hung external call without timeout

3b. Sling Job thread pool

Check Apache Sling Job Thread Pool in the Sling Thread Pools status page:

• active count vs max pool size
• If saturated, Sling Jobs cannot execute (workflow jobs stall)

3c. Granite Workflow Queue

Check the Sling Jobs page (/system/console/slingevent):

Check topic statistics for workflow model:

• Topic: com/adobe/granite/workflow/job/var/workflow/models/<modelName>
• High Failed Jobs / low Finished Jobs ratio → process step throwing exceptions

Check Granite Workflow Queue configuration:

• Type: Topic Round Robin
• Max Parallel: 0.5 OOTB on AEM 6.5 LTS (50% of available CPU cores). Increase for throughput on bursty workloads. Verify the running value at /system/console/configMgr/org.apache.sling.event.jobs.QueueConfiguration~workflow before assuming.
• Max Retries: 10

3d. Sling Scheduler

Check the Sling Scheduler status page (/system/console/status-slingscheduler):

• This page lists Quartz-style schedulers, not Sling Job topics. On OOTB AEM 6.5 LTS the workflow-related entry visible here is the periodic WorkflowStatsMBean collector (used by the Statistics MBean) — its nextFireTime should be in the near future; nextFireTime: null means the trigger was deregistered.
• The com/adobe/granite/workflow/timeout/job topic itself is a Sling Job, not a Quartz job — check it on the Sling Jobs page (/system/console/slingevent), not here.
• Confirm ApacheSlingdefault uses ThreadPool: default — that's how the periodic timeout-detection scheduler reaches the workflow engine.

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Step 4: Error log patterns

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Step 5: Configuration checklist

In Felix Console → OSGi → Configuration (/system/console/configMgr):

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Step 6: Remediation quick reference

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Step 7: Key JMX MBeans

All workflow maintenance and diagnostic operations live on a single MBean: com.adobe.granite.workflow:type=Maintenance. A separate MBean — com.adobe.granite.workflow:type=Statistics — exposes time-series workflow execution metrics for trend analysis.

Always use dryRun=true first before executing destructive purge or retry operations.

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Step 8: Common root cause patterns (from real incidents)

Pattern A: Thread pool starvation → auto-advance failure

Symptom: Workflow auto-advancement stops; timeout jobs not firing; workflows stuck at participant step despite timeout configured.

Root cause chain:

1. Custom scheduler (e.g. AccessTokenScheduler) makes blocking HTTP call without timeout
2. concurrent = true allows overlapping executions on each cron trigger
3. Each stuck execution consumes a default pool thread indefinitely
4. All pool threads consumed (OOTB on AEM 6.5 LTS that's only 5; environments hardened for throughput typically run with 20+) → pool saturated
5. If block policy has been changed to ABORT (OOTB is RUN), new Quartz triggers are rejected silently; on RUN they instead pile up on the caller thread and back-pressure the dispatch
6. The workflow timeout-detection scheduler cannot dispatch new com/adobe/granite/workflow/timeout/job events
7. Auto-advancement never happens

Diagnosis checklist:

• Sling Thread Pools page (/system/console/status-slingthreadpools): Pool default → active count = max pool size?
• Sling Thread Pools page: Pool default → block policy = ABORT?
• Threads page (/system/console/status-Threads) or jstack: All sling-default-* threads stuck on same stack?
• Sling Jobs page (/system/console/slingevent): Workflow job topic has high Failed Jobs?
• Sling Scheduler page (/system/console/status-slingscheduler): ThreadPool = default for ApacheSlingdefault?

Fix: Restart instance (immediate); fix scheduler code (add HTTP timeout, set concurrent=false); change pool policy to RUN; increase pool size.

Pattern B: High workflow job failure rate

Symptom: numberOfFailedJobs >> numberOfFinishedJobs for a workflow topic.

Root cause: Process step exception, payload deleted, or process not registered.

Diagnosis: Search error.log for Error executing workflow step + model name. Check process.label in Felix Console → OSGi Components.

Pattern C: Stale workflows accumulating

Symptom: Workflows in RUNNING state but no work items; Inbox empty despite running instances.

Root cause: Cannot archive workitem during transition; JCR session crash during step completion.

Diagnosis: Search for Cannot archive workitem; JMX countStaleWorkflows; restartStaleWorkflows(dryRun=true).

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References

• For runbook locations: see reference.md