Setting druid_segmentCache_locations causes a crash loop

I’ve deployed a Druid cluster to an EKS cluster. I did this by copying Druid’s sample Helm chart into my own project and making some edits.

I’ve managed to get the cluster up and running, and am enjoying playing around with the values.yaml file to get some basic query optimizations in place. But when I uncomment the druid_segmentCache_locations param, my historicals get stuck in a crash loop.

I’m still getting the hang of Kubernetes and I’m not too sure how to debug this, especially since the container crash deletes all of its log files. How do I identify what’s causing this issue?

Edit: I’m using the commented-out-by-default value for druid_segmentCache_locations:

druid_segmentCache_locations: '[{"path":"/var/druid/segment-cache","maxSize":300000000000}]'

The kubectl describe output for the failing pod:

Name:         druid-historical-0
Namespace:    dev
Priority:     0
Node:         ip-172-31-2-122.ec2.internal/
Start Time:   Fri, 20 May 2022 14:16:45 -0400
Labels:       app=druid
Annotations: eks.privileged
Status:       Running
Controlled By:  StatefulSet/druid-historical
    Container ID:  docker://fb6887b03ad67f1e5833994b1842b40d08770292942ab8fa468f51f6606e9f71
    Image:         apache/druid:0.22.0
    Image ID:      docker-pullable://apache/druid@sha256:626fd96a997361dce8452c68b28e935a2453153f0d743cf208a0b4355a4fc2c3
    Port:          8083/TCP
    Host Port:     0/TCP
    State:          Waiting
      Reason:       CrashLoopBackOff
    Last State:     Terminated
      Reason:       Error
      Exit Code:    1
      Started:      Fri, 20 May 2022 14:19:32 -0400
      Finished:     Fri, 20 May 2022 14:19:42 -0400
    Ready:          False
    Restart Count:  4
    Liveness:       http-get http://:8083/status/health delay=60s timeout=1s period=10s #success=1 #failure=3
    Readiness:      http-get http://:8083/status/health delay=60s timeout=1s period=10s #success=1 #failure=3
    Environment Variables from:
      druid  ConfigMap  Optional: false
      DRUID_XMS:                          8G
      DRUID_XMX:                          10G
      druid_processing_buffer_sizeBytes:  500000000
      druid_processing_numMergeBuffers:   4
      druid_processing_numThreads:        15
      druid_segmentCache_locations:       [{"maxSize":300000000000}]
      AWS_DEFAULT_REGION:                 us-east-1
      AWS_REGION:                         us-east-1
      AWS_ROLE_ARN:                       arn:aws:iam::552593679126:role/DruidEksStack-druidClusterdruidServiceAccountRole3-1H3W6KL1OZ6K5
      AWS_WEB_IDENTITY_TOKEN_FILE:        /var/run/secrets/
      /opt/druid/var/druid/ from data (rw)
      /var/run/secrets/ from aws-iam-token (ro)
      /var/run/secrets/ from kube-api-access-5mhmf (ro)
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  86400
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  data-druid-historical-0
    ReadOnly:   false
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              role=data-server
                    op=Exists for 300s
                    op=Exists for 300s
  Type     Reason                  Age                    From                     Message
  ----     ------                  ----                   ----                     -------
  Normal   Scheduled               13m                   default-scheduler        Successfully assigned dev/druid-historical-0 to ip-172-31-2-122.ec2.internal
  Normal   SuccessfulAttachVolume  13m                   attachdetach-controller  AttachVolume.Attach succeeded for volume "pvc-e32e6f48-55cd-4414-b503-c623c53026de"
  Normal   Pulling                 12m                   kubelet                  Pulling image "apache/druid:0.22.0"
  Normal   Pulled                  12m                   kubelet                  Successfully pulled image "apache/druid:0.22.0" in 12.084762823s
  Normal   Created                 10m (x5 over 12m)     kubelet                  Created container druid
  Normal   Started                 10m (x5 over 12m)     kubelet                  Started container druid
  Normal   Pulled                  10m (x4 over 12m)     kubelet                  Container image "apache/druid:0.22.0" already present on machine
  Warning  BackOff                 2m38s (x45 over 12m)  kubelet                  Back-off restarting failed container

Not sure why it is failing but you should be able to see the crashed pod’s log by using:
kubectl logs <podname> --previous

Here’s a broader discussion on the subject:

Hi James,

I realized I misread your post. Please try reducing the number to fit within your PVC.

Ahh ok, for some reason I had assumed that getting the pod’s logs wouldn’t tell me what happened in the container! Silly thing to assume in retrospect.

Looks like it’s failing to create the segment cache directory:

java.lang.reflect.InvocationTargetException: null
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_275]
        at sun.reflect.NativeMethodAccessorImpl.invoke( ~[?:1.8.0_275]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke( ~[?:1.8.0_275]
        at java.lang.reflect.Method.invoke( ~[?:1.8.0_275]
        at$AnnotationBasedHandler.start( ~[druid-core-0.22.0.jar:0.22.0]
        at ~[druid-core-0.22.0.jar:0.22.0]
        at org.apache.druid.guice.LifecycleModule$2.start( ~[druid-core-0.22.0.jar:0.22.0]
        at org.apache.druid.cli.GuiceRunnable.initLifecycle( [druid-services-0.22.0.jar:0.22.0]
        at [druid-services-0.22.0.jar:0.22.0]
        at org.apache.druid.cli.Main.main( [druid-services-0.22.0.jar:0.22.0]
Caused by: Failed to create directory[/var/druid/segment-cache/info_dir].
        at org.apache.druid.server.coordination.SegmentLoadDropHandler.loadLocalCache( ~[druid-server-0.22.0.jar:0.22.0]
        at org.apache.druid.server.coordination.SegmentLoadDropHandler.start( ~[druid-server-0.22.0.jar:0.22.0]
        ... 10 more

How much segment Storage (segmentCacheVolume) is requested in your yaml?

Hi Vijeth! I’m requesting 100 GiB.

Also, I figured out the issue! Just had to set the base of the path to ~:

druid_segmentCache_locations: '[{"path":"~/var/druid/segment-cache","maxSize":100000000000}]'

I noticed that this is where the segment cache is being written on a successful pod deploy. So it looks like it was just a permissions issue.

That makes sense. Thank you for letting us know the RCA