Kube-probe HTTP probe failed with status code 502

The application is acting as a gateway or proxy and received an invalid response from the upstream server.

Understanding Kube-probe

Kube-probe is a diagnostic tool used in Kubernetes to monitor the health of applications running in a cluster. It helps ensure that applications are running smoothly by performing health checks and reporting any issues. Kube-probe can perform HTTP, TCP, and command-based checks to determine the status of an application.

Identifying the Symptom

When using Kube-probe, you might encounter an error message stating: HTTP probe failed with status code 502. This indicates that the probe attempted to connect to an application endpoint but received a 502 Bad Gateway response.

Understanding the 502 Error Code

What is a 502 Bad Gateway?

The 502 status code means that the application, acting as a gateway or proxy, received an invalid response from an upstream server. This typically occurs when the upstream server is down, misconfigured, or unable to handle the request.

Common Causes of 502 Errors

Upstream server is unavailable or down.
Network connectivity issues between the proxy and upstream server.
Misconfigured proxy settings.

Steps to Resolve the Issue

1. Investigate the Upstream Server

Start by checking the status of the upstream server. Ensure it is running and capable of handling requests. You can use the following command to check the status of a service in Kubernetes:

kubectl get pods -l app=your-upstream-app

Replace your-upstream-app with the label of your upstream application.

2. Check Network Connectivity

Ensure that there are no network issues preventing the proxy from communicating with the upstream server. You can test connectivity using:

kubectl exec -it your-proxy-pod -- ping your-upstream-service

Replace your-proxy-pod and your-upstream-service with the appropriate pod and service names.

3. Review Proxy Configuration

Check the configuration of the proxy to ensure it is correctly set up to forward requests to the upstream server. Look for any misconfigurations in the proxy settings.

Additional Resources

For more information on troubleshooting Kubernetes applications, you can refer to the following resources:

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MORE ISSUES

Kube-probe Probe failed: invalid probe configuration

The probe configuration contains invalid parameters or syntax errors.

Kube-probe Probe failed: invalid response length

The application returned a response with an unexpected length.

Kube-probe Exec probe failed: file not found

The file required by the exec probe command is not present in the container.

Kube-probe TCP probe failed: address in use

The port specified for the TCP probe is already in use by another process.

Kube-probe Probe failed: invalid character encoding

The application returned a response with an unexpected character encoding.

Kube-probe HTTP probe failed with status code 429

The application is rate limiting requests and the probe exceeded the limit.

Kube-probe Liveness probe failed: application out of memory

The application has run out of memory and cannot respond to the probe.

Kube-probe Readiness probe failed: application misconfiguration

The application is misconfigured and cannot become ready.

Kube-probe HTTP probe failed with status code 405

The application does not allow the HTTP method used by the probe.

Kube-probe Exec probe failed: insufficient memory

The command executed by the exec probe requires more memory than available.

Kube-probe Probe failed: invalid JSON response

The application returned a JSON response that is not well-formed.

Kube-probe HTTP probe failed with status code 408

The application took too long to respond to the probe request.

Kube-probe Liveness probe failed: application deadlock

The application is in a deadlock state and cannot respond to the probe.

Kube-probe TCP probe failed: protocol error

There is a protocol mismatch between the probe and the application.

Kube-probe Probe failed: invalid SSL certificate

The SSL certificate used by the application is invalid or expired.

Kube-probe Probe failed: invalid content type

The application returned a response with an unexpected content type.

Kube-probe Readiness probe failed: application initialization error

The application failed to initialize properly.

Kube-probe Probe failed: invalid response code

The application returned an unexpected HTTP status code.

Kube-probe HTTP probe failed with status code 302

The application is redirecting the probe request temporarily.

Kube-probe Exec probe failed: environment variable missing

The command executed by the exec probe relies on an environment variable that is not set.

Kube-probe HTTP probe failed with status code 400

The application received a bad request from the probe.

Kube-probe TCP probe failed: host unreachable

The probe cannot reach the host due to network issues.

Kube-probe Probe failed: invalid header format

The probe is sending headers in an incorrect format.

Kube-probe HTTP probe failed with status code 404

The HTTP probe is trying to access a path that does not exist on the application.

Kube-probe Probe failed: unsupported protocol

The probe is attempting to use a protocol not supported by the application.

Kube-probe Liveness probe failed: resource starvation

The application is unable to respond to the probe due to lack of resources.

Kube-probe Probe failed: malformed URL

The URL specified in the probe configuration is not correctly formatted.

Kube-probe HTTP probe failed with status code 301

The application is redirecting the probe request to a different URL.

Kube-probe Readiness probe failed: dependency service down

A dependent service required by the application is not available.

Kube-probe Exec probe failed: exit code non-zero

The command executed by the exec probe returned a non-zero exit code, indicating failure.

Kube-probe TCP probe failed: connection timed out

The probe is unable to establish a connection to the application within the timeout period.

Kube-probe Probe failed: invalid HTTP method

The probe is using an HTTP method that the application does not support.

Kube-probe HTTP probe failed with status code 503

The application is temporarily unavailable, possibly due to overload or maintenance.

Kube-probe Probe failed: SSL handshake error

There is an issue with the SSL/TLS configuration between the probe and the application.

Kube-probe Liveness probe failed: application crash

The application has crashed and is unable to respond to the liveness probe.

Kube-probe Readiness probe failed: resource limit exceeded

The application is unable to allocate necessary resources to handle the probe request.

Kube-probe TCP probe failed: network unreachable

The network is not properly configured, preventing the probe from reaching the application.

Kube-probe Probe failed: invalid response format

The application returned a response in an unexpected format that the probe cannot interpret.

Kube-probe Exec probe failed: permission denied

The command specified in the exec probe lacks the necessary permissions to execute.

Kube-probe HTTP probe failed with status code 502

The application is acting as a gateway or proxy and received an invalid response from the upstream server.

Kube-probe HTTP probe failed with status code 403

The application is denying access to the probe due to insufficient permissions.

Kube-probe HTTP probe failed with status code 401

The probe is not authenticated to access the endpoint.

Kube-probe Readiness probe failed: service unavailable

The application is not ready to serve traffic.

Kube-probe Liveness probe failed: container not running

The container has crashed or is not running.

Kube-probe Probe failed: DNS resolution error

The probe is unable to resolve the DNS name of the application.

Kube-probe Probe failed: no route to host

Network connectivity issues between the probe and the application.

Kube-probe Exec probe failed: command not found

The command specified in the exec probe is not available in the container's environment.

Kube-probe Liveness probe failed: HTTP 500

The application is returning an internal server error for the liveness probe request.

Kube-probe TCP probe failed: connection refused

The application is not listening on the specified port, or the service is not running.

Kube-probe Readiness probe failed: timeout

The application is taking too long to respond to the readiness probe.

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