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Pod HTTP modify header

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Pod HTTP modify header is a Kubernetes pod-level chaos fault that overrides HTTP request or response headers on the target pod for a configurable duration. You provide a map of header keys to values that the proxy then injects, replaces, or removes (when the value is empty). When the fault ends, headers return to normal immediately.

Use this fault to test how a client or server behaves when a header it depends on is missing, malformed, or carries an unexpected value: a missing Authorization, a flipped Cache-Control, a removed Content-Type, or a tampered correlation ID.

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:

  • Authentication header tampering: Removing Authorization from the request or modifying its value verifies whether the server returns a clean 401 or leaks information about authentication failures.
  • Cache directive resilience: Flipping Cache-Control from no-store to max-age=3600 on responses reveals whether intermediate caches store sensitive data they should not.
  • Tracing and correlation IDs: Stripping X-Request-ID or traceparent shows whether logs and traces still correlate, or whether the request becomes invisible to observability.
  • Content-type coercion: Changing Content-Type from application/json to text/html exposes clients that select parsers based on the header.
  • Custom security headers: Removing X-Frame-Options, Content-Security-Policy, or Strict-Transport-Security from responses verifies whether browsers and downstream services degrade safely.

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).
  • HTTP service on a known port: The target container serves HTTP, HTTPS, or gRPC traffic on a port you can specify with TARGET_SERVICE_PORT.
  • 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

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

Fault tunables​

Configure the following fault parameters when you add Pod HTTP modify header to an experiment in Chaos Studio. Defaults are shown for reference.

Chaos parameters

TunableDescriptionDefault
HEADERS_MAPJSON object of header key-value pairs to inject or replace. Set a value to "" to remove that header. Example: {"X-Auth-Token":"deadbeef","X-Trace-Id":""}.{}
HEADER_MODEWhether to modify request headers (sent to the server) or response headers (sent to the client).response
TARGET_SERVICE_PORTPort the target container listens on for HTTP traffic.80
TOXICITYPercentage of intercepted messages whose headers are modified, between 0 and 100. 100 modifies every matching message.100
TOTAL_CHAOS_DURATIONDuration of the fault in seconds.60

Proxy and interface

TunableDescriptionDefault
PROXY_PORTPort the chaos proxy listens on inside the container's network namespace. Must not conflict with any port already in use on the target container.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.

Removing a header

Set the header's value in HEADERS_MAP to an empty string to remove the header. For example, {"Authorization":""} removes the Authorization header rather than setting it to an empty value.

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 HTTP traffic on TARGET_SERVICE_PORT inside the container's network namespace and rewrites headers on either the request or response stream (as configured by HEADER_MODE) using the entries in HEADERS_MAP, optionally limited to a percentage of messages so other traffic is unaffected.

Expected behavior during fault execution​

  • HTTP and HTTPS messages on TARGET_SERVICE_PORT are rewritten according to HEADER_MODE and HEADERS_MAP. Existing headers with matching keys are replaced; new headers are added; headers with an empty value in the map are removed.
  • Only messages selected by TOXICITY are modified; the rest pass through unchanged. Bodies, status codes, and other headers are preserved.
  • Traffic on other ports of the same container is not affected. gRPC headers and trailers carried over HTTP/2 are modified the same way.
  • Clients or servers that fail validation on missing or unexpected headers surface their own error responses (often 400 or 401); ones that silently fall back may continue to operate, which is itself a finding.
When the fault ends

After TOTAL_CHAOS_DURATION, the proxy is torn down and headers return to their original values within a couple of seconds. In-flight messages already buffered for modification are released as soon as cleanup runs.

Signals to watch​

Attach resilience probes to assert each layer:

  • Client error rate: Use an HTTP probe on the calling service to detect 4xx responses driven by missing or unexpected headers.
  • Authentication and authorization metrics: Use a Prometheus probe on auth failure counters when modifying Authorization or session headers.
  • Trace continuity: Use a command probe to query your tracing system for orphan spans during the experiment window.

Verify the fault execution effect​

While the experiment is running, confirm the headers are being rewritten:

  1. Inspect headers returned to a client (when HEADER_MODE=response).

    kubectl run -n <namespace> tester --image=curlimages/curl --rm -it -- \
      curl -i http://<target-pod-ip>:<TARGET_SERVICE_PORT>/<known-path>

    The response headers should reflect HEADERS_MAP: added or modified keys present with the configured values, removed keys absent.

  2. Inspect headers received by the server (when HEADER_MODE=request).

    Have the target application log the incoming request headers (or use an echo endpoint) and confirm the modifications appear there. Status codes, the response body, and headers outside HEADERS_MAP should be unchanged.

Recovery and cleanup​

  • End of duration: The proxy is removed automatically and HTTP headers return to their original values.
  • 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 supplied certificates: This fault does not terminate TLS. If the target serves HTTPS and you need to modify encrypted headers, use Pod API modify header, which accepts CA, server, and client certificates as TLS inputs.
  • Pseudo-headers (HTTP/2 :method, :path, :status, :authority): These cannot be modified through HEADERS_MAP. Use other faults (such as Pod HTTP status code) to control them.
  • Hop-by-hop headers: Headers like Connection and Transfer-Encoding are owned by the proxy itself and are not safe to override through HEADERS_MAP.
  • Port already bound: If PROXY_PORT collides with a port the target container is already using, the fault fails to start. Pick a port number outside the application's range.

Troubleshooting​

Pod HTTP modify header 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.

Headers are unchanged during pod-http-modify-header

The most common causes are: TARGET_SERVICE_PORT does not match the port the application actually listens on (verify with kubectl exec <pod> -- ss -tlnp); HEADER_MODE is set to response but you are inspecting request headers (or vice versa); the traffic is HTTPS and the chaos proxy is not terminating TLS (use Pod API modify header instead); or HEADERS_MAP is not valid JSON. Re-run with TOXICITY=100 and a minimal one-entry HEADERS_MAP to confirm the path is working.

Connection to container runtime fails for pod-http-modify-header in Harness Chaos Engineering

The default SOCKET_PATH is /run/containerd/containerd.sock. For Docker, set CONTAINER_RUNTIME=docker and SOCKET_PATH=/var/run/docker.sock. For CRI-O, set CONTAINER_RUNTIME=crio and SOCKET_PATH=/var/run/crio/crio.sock.

Headers remain modified after pod-http-modify-header 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.