Agent Troubleshooting

Diagnose why jobs aren't being picked up by agents.

When to use

• "My build is stuck waiting for an agent"
• "Jobs aren't being picked up"
• "Why is my build stuck in scheduled?"
• "Agent not running my job"
• "Queue issues"
• "No agents available"

Available MCP Tools

Input Parsing

User typically describes a symptom:

Get the build number/URL to investigate.

Approach

1. Get the build with buildkite_get_build

   • Find the stuck job
   • Note its state (scheduled, assigned, etc.)
   • Extract agent query rules (queue, tags)

2. Check cluster/queue configuration

   • List clusters with buildkite_list_clusters
   • List queues with buildkite_list_cluster_queues
   • Get queue stats with buildkite_get_cluster_queue

3. Compare requirements vs availability

   • What does the job require?
   • What agents/queues exist?
   • Where's the mismatch?

4. Provide diagnosis and fix

Job States for Agent Issues

Jobs stuck in scheduled = agent matching problem.

Common Issues

1. Queue Mismatch

Symptom: Job stuck in scheduled Cause: Job requires queue that doesn't exist or has no agents

# Pipeline requires:
agents:
  queue: "deploy"

# But no agents are in the "deploy" queue

Diagnosis:

Job requires: queue=deploy
Available queues: default (5 agents), build (10 agents)
❌ No "deploy" queue exists

Fix: Add agents to the deploy queue, or change pipeline to use existing queue.

2. Tag Mismatch

Symptom: Job stuck in scheduled Cause: Job requires tags no agent has

# Pipeline requires:
agents:
  queue: "default"
  docker: "true"
  os: "linux"

# Agents have docker=true but os=macos

Diagnosis:

Job requires: queue=default, docker=true, os=linux
Available agents in default:
  - agent-1: docker=true, os=macos
  - agent-2: docker=true, os=macos
❌ No agent matches os=linux

Fix: Add Linux agents, or remove the os requirement.

3. No Agents Running

Symptom: Job stuck in scheduled Cause: Queue exists but no agents connected

Diagnosis:

Job requires: queue=deploy
Queue "deploy" exists but has 0 connected agents

Fix: Start agents, check agent host health, verify network connectivity.

4. All Agents Busy

Symptom: Job stuck in scheduled longer than usual Cause: Agents exist but at capacity

Diagnosis:

Job requires: queue=default
Queue "default": 3 agents, 15 jobs waiting
Average wait time: 12 minutes

Fix: Scale up agents, reduce parallelism, or wait.

5. Agent Assigned But Not Starting

Symptom: Job stuck in assigned state Cause: Agent accepted job but can't start it

Possible causes:

• Agent hooks failing (environment, pre-command)
• Plugin installation failing
• Disk space issues
• Agent process problems

Fix: Check agent logs on the host machine.

Response Format

## Agent Issue Diagnosed

**Build**: #456
**Stuck Job**: "Run Tests"
**State**: scheduled (waiting for agent)

### Job Requirements
- Queue: `deploy`
- Tags: `docker=true`

### Available Resources
- Queue `deploy`: ❌ Does not exist
- Queue `default`: 5 agents (none match)

### Root Cause
The job requires `queue=deploy` but no such queue exists in your cluster.

### Fix
**Immediate**: Change the pipeline to use `queue=default`:
```yaml
agents:
  queue: "default"
  docker: "true"
```

**Long-term**: Create a `deploy` queue and add dedicated agents for deployments.

Diagnostic Commands

When explaining fixes, reference these Buildkite agent commands:

# Check agent status
buildkite-agent status

# See what queues/tags an agent has
buildkite-agent start --tags "queue=deploy,docker=true"

# Check agent logs
journalctl -u buildkite-agent

Example Interaction

User: My build is stuck waiting for an agent

1. Ask for build URL/number
2. Fetch build, find stuck job in "scheduled" state
3. Extract agent requirements: queue=special, gpu=true
4. List queues - "special" exists with 2 agents
5. Check queue details - agents have gpu=false
6. Explain: "Job needs gpu=true but queue agents don't have GPU tag"
7. Suggest: Add GPU agents or modify job requirements