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Pod API status code

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Pod API status code is a Kubernetes pod-level chaos fault that overrides the HTTP status code returned by selected API calls on the target pod for a configurable duration. You can also overwrite the response body to match the new status. It accepts the same rich filter set as other API faults (path, method, headers, query, source, destination) and supports HTTPS through user-supplied TLS certificates. When the fault ends, status codes return to whatever the application produces naturally.

Use this fault to test client error handling on specific endpoints: return 429 only on a rate-limited path, force 503 on calls to one upstream, or simulate 401 on the auth refresh endpoint.

Run your first experiment

If you have not configured the chaos infrastructure yet, go to Quickstart to install the chaos infrastructure and run an experiment end to end.

Use cases​

Run this fault when you want to answer concrete questions like:

  • Path-scoped error injection: Return 503 only on PATH_FILTER=/v2/checkout to test that other endpoints continue serving traffic while one degrades.
  • Retry classification: Does the client retry on 503 but not on 400? Does it honor Retry-After on 429?
  • Tenant-scoped failure: Use HEADERS_FILTERS=X-Tenant: prod-eu to return 429 only to one tenant's calls.
  • Error budget burn: Force a calibrated percentage of 500s on a specific endpoint to validate your SLO alerting.
  • Auth token expiry simulation: Return 401 on the user-info endpoint to verify the client refreshes its token instead of looping.

Prerequisites​

  • Kubernetes version: 1.21 or later. Go to What's supported to confirm distribution support.
  • Target pods are Running: The application pods you intend to target are in the Running state before the fault is launched.
  • Privileged pods allowed: The cluster lets you schedule privileged pods in the chaos namespace. GKE Autopilot supports this fault but requires the one-time setup in Chaos on GKE Autopilot; other locked-down distributions may need similar exemptions.
  • Container runtime access: The chaos pod can reach the container runtime socket on the target node (/run/containerd/containerd.sock, /var/run/docker.sock, or /var/run/crio/crio.sock).
  • API service on a known port: The target container serves HTTP, HTTPS, or gRPC traffic on a port you can specify with TARGET_SERVICE_PORT.
  • TLS material for HTTPS targets: When HTTPS_ENABLED=true, you provide CA, server, and (optionally) client certificate secrets so the proxy can terminate TLS and apply filters.
  • Workload selector defined: The chaos experiment knows the target workload by kind, namespace, and either names or labels.

Supported environments​

PlatformSupport status
Amazon EKSSupported
Azure AKSSupported
Google GKESupported
Red Hat OpenShiftSupported
RancherSupported
VMware TanzuSupported
Self-managed Kubernetes (CNCF-certified)Supported
GKE AutopilotSupported with Autopilot setup
EKS Fargate, ACI virtual nodesNot supported (no access to container runtime sockets)

Permissions required​

The fault runs under the chaos infrastructure's service account.

Resource (apiGroup)VerbsWhy it is needed
pods ("")get, list, create, delete, deletecollection, patch, updateDiscover target pods and run the chaos pod on the same node
pods/log ("")get, list, watchStream chaos pod logs for status and debugging
deployments, statefulsets, replicasets, daemonsets (apps)get, listResolve the target workload to the pods it owns
events ("")get, list, create, patch, updateRecord fault progress as Kubernetes events
jobs (batch)get, list, create, delete, deletecollectionRun the chaos job that drives the fault
secrets ("")get, listRead TLS certificate secrets when HTTPS_ENABLED=true

The default Harness chaos infrastructure service account already includes these permissions.

Fault tunables​

Configure the following fault parameters when you add Pod API status code to an experiment in Chaos Studio. Defaults are shown for reference.

Chaos parameters

TunableDescriptionDefault
STATUS_CODEHTTP status code to return. 0 picks one at random from the supported set (200, 201, 202, 204, 300, 301, 302, 304, 307, 400, 401, 403, 404, 500, 501, 502, 503, 504).0
RESPONSE_BODYBody to return alongside the modified status code. Empty falls back to a default body matching the status.""
TRANSACTION_PERCENTAGEPercentage of matched API calls whose status is overridden, between 0 and 100.0
TARGET_SERVICE_PORTPort the target container listens on for API traffic.80
TOTAL_CHAOS_DURATIONDuration of the fault in seconds.60

Filters (API matching)

All filters are optional. Leave empty to match everything in that dimension. Combining filters narrows the match (AND across dimensions).

TunableDescriptionDefault
PATH_FILTERURL path the fault matches. Empty matches all paths.""
METHODSComma-separated HTTP methods to match (for example GET,POST). Empty matches all methods.""
QUERY_PARAMSQuery-parameter filter. Empty matches all query strings.""
HEADERS_FILTERSHeader filter used to match incoming calls. Empty matches all headers.""

Filters (traffic source and destination)

TunableDescriptionDefault
SERVICE_DIRECTIONWhether to filter ingress traffic (received by the pod) or egress traffic (sent from the pod).ingress
SOURCE_HOSTSHostnames of the calling client (ingress only). Empty matches any source.""
SOURCE_IPSSource IPs of the calling client (ingress only). Empty matches any source.""
DESTINATION_HOSTSDestination hostnames for the call (egress only). Empty matches any destination.""
DESTINATION_IPSDestination IPs for the call (egress only). Empty matches any destination.""
DESTINATION_PORTSComma-separated destination ports (egress only). Empty matches any port.""

TLS (for HTTPS targets)

TunableDescriptionDefault
HTTPS_ENABLEDSet to true when the target serves HTTPS so the proxy terminates TLS to apply filters.false
CA_CERTIFICATESKubernetes secret holding the Base64-encoded CA certificate (ca.key, ca.crt).""
SERVER_CERTIFICATESSecret holding the Base64-encoded server certificate (server.key, server.crt).""
CLIENT_CERTIFICATESSecret holding the Base64-encoded client certificate (client.key, client.crt) for mTLS upstreams.""

Proxy and interface

TunableDescriptionDefault
PROXY_PORTPort the chaos proxy listens on inside the container's network namespace.20000
NETWORK_INTERFACENetwork interface inside the target container's namespace. Almost always eth0 for standard CNI plugins.eth0

Targeting

TunableDescriptionDefault
TARGET_PODSComma-separated list of pod names to target. Empty selects from the workload's pods using POD_AFFECTED_PERCENTAGE.""
TARGET_CONTAINERContainer in the pod whose network namespace to enter. Empty targets the first container in the pod spec.""
NODE_LABELLabel selector to filter target pods by the node they run on. Empty disables node-based filtering.""
POD_AFFECTED_PERCENTAGEPercentage of the workload's pods to target. 0 means one pod.0
SEQUENCEWhen multiple pods are targeted, inject parallel (all at once) or serial (one after another).parallel

Runtime and helper

TunableDescriptionDefault
CONTAINER_RUNTIMEContainer runtime on the target nodes. One of containerd, docker, crio.containerd
SOCKET_PATHPath to the container runtime socket on the target node. Set to match CONTAINER_RUNTIME./run/containerd/containerd.sock
RAMP_TIMEWait period in seconds before and after the fault. Go to ramp time to read how it is applied.0

Tunables that apply to every chaos fault are documented in common tunables for all faults.

Combine STATUS_CODE with RESPONSE_BODY for realistic errors

Returning 429 with a body like {"error":"rate_limited","retry_after":30} (and the matching Retry-After header set via Pod API modify header or Pod API modify response custom) more closely matches what a real rate-limited upstream would send.

Configure for your container runtime​

Set CONTAINER_RUNTIME and SOCKET_PATH to match the runtime on the target node:

CONTAINER_RUNTIMESOCKET_PATH
containerd (default)/run/containerd/containerd.sock
docker/var/run/docker.sock
crio/var/run/crio/crio.sock

Fault execution in brief​

Intercepts API responses on TARGET_SERVICE_PORT inside the container's network namespace and replaces the status code with STATUS_CODE (and optionally rewrites the body with RESPONSE_BODY) for the configured percentage of calls that match the path, method, header, query, and source or destination filters, optionally terminating TLS to apply the same logic to HTTPS calls.

Expected behavior during fault execution​

  • API responses for calls that match every configured filter return STATUS_CODE instead of the application's original status. When RESPONSE_BODY is non-empty it replaces the body; otherwise a default body matching the status code is returned.
  • Calls outside the filter set return the application's normal status code unchanged. Only the percentage selected by TRANSACTION_PERCENTAGE is modified.
  • For HTTPS targets, the proxy terminates TLS using the supplied certificates so it can intercept responses.
  • Clients that branch on status codes execute their corresponding error-handling paths: retry, fail-fast, refresh tokens, back off, and so on.
When the fault ends

After TOTAL_CHAOS_DURATION, the proxy is torn down and API status codes return to whatever the application produces.

Signals to watch​

Attach resilience probes to assert each layer:

  • Status-code distribution per path: Use a Prometheus probe on http_requests_total{path="...",status="..."} to confirm the injected codes match STATUS_CODE only on the filtered path.
  • Client retry counter: Use a Prometheus probe on the calling service's retry counter to verify it backs off correctly.
  • End-user error rate: Use an HTTP probe against the top-level API to detect whether injected errors leak through to end users.

Verify the fault execution effect​

While the experiment is running, confirm the status code is being overridden on the right calls:

  1. Make a matched request and inspect the status line.

    kubectl run -n <namespace> tester --image=curlimages/curl --rm -it -- \
      curl -i -X <METHOD> "http://<target-pod-ip>:<TARGET_SERVICE_PORT><PATH_FILTER>"

    The status line should equal HTTP/1.1 <STATUS_CODE> ... on at least TRANSACTION_PERCENTAGE percent of matched calls.

  2. Confirm an unmatched call returns the application's original status.

    A call to a different path or method should return the application's normal status code unchanged.

Recovery and cleanup​

  • End of duration: The proxy is removed automatically and API status codes return to baseline.
  • Abort the experiment: Stopping the experiment from Chaos Studio triggers the same cleanup path.
  • Failed cleanup: If automated cleanup did not complete, restart the target pod to reset its network state.

Limitations​

  • Serverless Kubernetes (EKS Fargate, ACI virtual nodes): These platforms do not expose container runtime sockets and reject the privileged access the fault needs. GKE Autopilot is supported once the one-time setup in Chaos on GKE Autopilot is in place.
  • Windows containers: This fault is supported on Linux pods only.
  • HTTPS without certificates: When HTTPS_ENABLED=true, the proxy must terminate TLS. If the supplied certificates do not chain to one the client trusts, the client refuses the connection before any filter is applied.
  • gRPC status: gRPC carries status in HTTP/2 trailers (grpc-status), not the HTTP status line. This fault overrides the HTTP status; gRPC clients also check grpc-status and may behave differently.
  • Status codes outside the supported set: Only the codes listed under STATUS_CODE are supported.
  • Port already bound: If PROXY_PORT collides with a port the target container is already using, the fault fails to start.

Troubleshooting​

Pod API status code experiment stays Pending or never starts in Harness Chaos Engineering

Inspect the chaos pods in the experiment namespace with kubectl describe pod -n <chaos-namespace>. The most common causes are taints on the target node that the chaos pods do not tolerate, insufficient resources, or a PodSecurity admission policy blocking privileged pods. Add the required tolerations to the experiment or run in a namespace with privileged Pod Security level.

Status code is unchanged during pod-api-status-code

The most common causes are: TRANSACTION_PERCENTAGE is 0 (default) so no calls are modified; STATUS_CODE is outside the supported list; filters are over-specified and match no real traffic; HTTPS_ENABLED is false but the target serves HTTPS; or the supplied TLS certificates do not chain correctly. Re-run with TRANSACTION_PERCENTAGE=100, STATUS_CODE=503, and a single broad filter to confirm the path.

TLS handshake fails for pod-api-status-code in Harness Chaos Engineering

Verify the secrets referenced by CA_CERTIFICATES, SERVER_CERTIFICATES, and CLIENT_CERTIFICATES exist in the chaos namespace and contain Base64-encoded key/crt pairs (ca.key/ca.crt, server.key/server.crt, client.key/client.crt). The server certificate must include the target pod's service name in its SAN list.

Status code overrides persist after pod-api-status-code ends

Automated cleanup did not complete. Restart the target pod to reset its network state. If the issue recurs, capture the chaos pod logs from the experiment namespace before the next run and share them with Harness support.