audit-forwarder

Audit-forwarder

This is a small piece of software that is intended to run as sidecar in an out-of-cluster kube-apiserver (for example: gardener clusters) and forward the audit log data back into the cluster where it can be picked up by cluster monitoring / logging software.

Current scope for the implementation

• The audit-forwarder has to run as sidecar container of the kube-apiserver
• The audit data needs to be logged to file in a shared volume
• There has to be a corresponding kubernetes-audit-tailer service and pod in the cluster that receives the audit data and makes it available to a cluster logging solution, e.g. by writing it to its stdout so that it appears as container log
• We use fluent-bit with the forward out plugin as forwarding agent because it is built for the task of reliably forwarding log data. There needs to be a corresponding fluent-bit or fluentd running in the kubernetes-audit-tailer pod to receive the data

Use with proxy (mTLS proxy with http-connect)

In some scenarios it is necessary to use a proxy to communicate from the control plane to the cluster:

• When a konnectivity proxy is used to connect from the control plane to the cluster. Konnectivity comes in two flavours:
  • Using a UDS proxy
  • Using a mTLS proxy with http-connect
• When the Gardener reversed-vpn feature is used

Auditforwarder can use either UDS or mTLS proxy; konnectivity or Gardener reversed-vpn look the same from a user perspective (only the proxy hostname is different) so they get treated the same.

FIXME describe this better

• A UDS proxy using the http connect method, running in another sidecar of the apiserver. Details on how this gets invoked are within the konnectivity test case (see next section).
• A mTLS proxy using http connect, running in a seperate pod from the kube-apiserver. The method to use this is much the same as with the UDS proxy; there are seperate command options to specify the proxy host and port.

Testing locally

Test cases for local testing in a kind cluster can be found in the kind subdirectory.