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Coredump REST API for Kubernetes

koredump enables easy access to core dumps in a Kubernetes cluster. REST API and command line tools are provided, that allow user to get information on core dumps in a cluster, and to download the core dump files.

Core dumps are captured and stored on disk by the infra platform, and koredump supports Red Hat OCP that uses the systemd-coredump service.

Design

  • In-cluster http://koreapi.koredump.svc.cluster.local:80 REST API (Kubernetes Service). One container per cluster, application listening port 5000.
  • One REST API server per node in k8s cluster (Kubernetes DaemonSet), listening port 5001.
  • No changes to platform core_pattern kernel config, use default systemd-coredump in OCP.
  • Access coredump files from /var/lib/systemd/coredump, and (optionally) read journal logs for full coredump metadata written by systemd-coredump.
  • DAC_OVERRIDE capability is used in container to access core dump files and journal logs.
  • Command line utility koredumpctl that uses the REST API. Automatically installed in OCP to /usr/local/bin/koredumpctl with Kubernetes init container.
  • Note that in OCP core dumps are deleted by default after 3 days (see systemd-tmpfiles --cat-config | grep core).
  • Collect all coredumps in cluster by default. Limit to predefined namespaces by setting filter.namespaceRegex variable when installing with Helm charts.
  • Token authentication for REST API. Server uses TokenReview to verify the token.

Limitations

  • Red Hat OCP privileged Security Context Constraint (SCC) is needed.
  • In-cluster traffic is unencrypted HTTP.
  • Simple implementation with python3.
  • Hard requirement on systemd-coredump, core files are processed from /var/lib/systemd/coredump directory only. Note that if core_pattern is set e.g. to /tmp/core or similar, the cores are written to container filesystem, and not visible via this tool.
  • Core file deletion not (yet) possible. (Host paths are read-only mounted into containers)
  • REST API can return errors during installation and upgrade, when the koredump PODs are being terminated or created.
  • systemd-coredump by default limits core size to maximum 2GB, larger core files are truncated. Increase the limit by setting for example ExternalSizeMax=32G in /etc/systemd/coredump.conf (or add conf file in /etc/systemd/coredump.conf.d/).

API Documentation

GET /apiv1/cores

JSON list of cores (metadata) available in cluster.

Example 
bash-5.1$ curl -fsS -H "Authorization: Bearer $token" koreapi/apiv1/cores | jq
[
  {
    "ARCH": "x86_64",
    "COREDUMP_CMDLINE": "/usr/bin/example -a -b -c",
    "COREDUMP_COMM": "example",
    ...
    "COREDUMP_SIGNAL": 24,
    "COREDUMP_SIGNAL_NAME": "SIGXCPU",
    "container": "ctr-ns1-example",
    "id": "core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4",
    "node": "ocp-example",
    "pod": "pod-ns1-example-86b5c54447-lrbz2"
  },
  {
    ...
  }
]

GET /apiv1/cores/metadata/<node>/<core_id>

JSON metadata of single core file, identified by kubernetes node name, and core file ID.

Example 
bash-5.1$ curl -fsS -H "Authorization: Bearer $token" koreapi/apiv1/cores/metadata/ocp-example/core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4 | jq
{
  "ARCH": "x86_64
  "COREDUMP_CMDLINE": "/usr/bin/example -a -b -c",
  "COREDUMP_COMM": "example",
  ...
  "COREDUMP_SIGNAL": 24,
  "COREDUMP_SIGNAL_NAME": "SIGXCPU",
  "container": "ctr-ns1-example",
  "id": "core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4",
  "node": "ocp-example",
  "pod": "pod-ns1-example-86b5c54447-lrbz2"
}

GET /apiv1/cores/download/<node>/<core_id>

Download core file, identified by kubernetes node name, and core file ID.

Example 
bash-5.1$ curl -fvsS -O -H "Authorization: Bearer $token" koreapi/apiv1/cores/download/ocp-example/core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4
* Connected to koreapi (172.30.199.84) port 80 (#0)
> GET /apiv1/cores/download/ocp-example/core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4 HTTP/1.1
> Host: koreapi
> User-Agent: curl/7.79.1
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Server: gunicorn
< Date: Fri, 14 Jan 2022 05:48:11 GMT
< Connection: close
< Content-Disposition: attachment; filename=core.example.9999.f1c1b6957ac9436d9113a86c8c905508.141241.1642081018000000.lz4
< Content-Type: application/octet-stream
< Content-Length: 279816
< Last-Modified: Thu, 13 Jan 2022 12:29:50 GMT
< Cache-Control: no-cache
< 
* Closing connection 0

Install and run in Red Hat OCP

Install (in Red Hat OCP as core user):

oc new-project koredump
helm repo add koredump https://nokia.github.io/koredump/
helm repo update
helm install -n koredump koredump koredump/koredump
watch kubectl -n koredump get all

Upgrade:

helm repo update
helm upgrade -n koredump koredump koredump/koredump
watch kubectl -n koredump get all

Test with koredumpctl:

koredumpctl status
koredumpctl list

Example koredumpctl list output:

$ koredumpctl list
- ID: core.prog.0.e36680b3d32e4f4f9899d72d34fe5fb3.207856.1638186984000000.lz4
  Node: ocp-6
  Pod: po-prog-oam-0
  Container: ctr-prog
  Namespace: demo
  Image: image-registry.openshift-image-registry.svc:5000/demo/prog:1.2.0
  Signal: SIGXCPU (24)
  Timestamp: 2022-02-23T08:23:16Z
- ID: core.stunnel.9999.29162cb2ca0d4e1eb67a4ffb549ed670.2354652.1645604596000000.lz4
  Node: ocp-6
  Pod: po-cran1-stunnel-d897f48fd-8q68m
  Container: ctr-cran1-stunnel
  Namespace: demo
  Image: image-registry.openshift-image-registry.svc:5000/demo/stunnel:2.4.0
  Signal: SIGXCPU (24)
  Timestamp: 2022-02-23T08:23:16Z

Uninstall:

helm uninstall koredump
rm /usr/local/bin/koredumpctl

Development Notes

Install from git repository:

git clone https://github.com/nokia/koredump.git
cd koredump
oc new-project koredump
helm install koredump charts/koredump/
watch kubectl get all

Run API servers locally without Kubernetes, for example in Fedora:

NO_TOKENS=1 FLASK_ENV=development PORT=5001 DAEMONSET=1 FAKE_K8S=1 gunicorn --access-logfile=- app
NO_TOKENS=1 FLASK_ENV=development PORT=5000 KOREDUMP_DAEMONSET_PORT=5001 DAEMONSET=0 FAKE_K8S=1 gunicorn --access-logfile=- app

Links