kube-log-runner (formerly known as go-runner)

The kube-log-runner is a Go based binary that can run commands and redirect stdout/stderr etc.

Why do we need this?

• Some of our images like kube-apiserver used bash output redirection for collecting logs, so we were not able to switch to distroless images directly for these images. The klog's --log-file parameter was supposed to fix this problem, but we ran into trouble with that in scalability CI jobs that never could get root caused and fixed. Using this binary worked.

• Windows services don't have a mechanism for redirecting output of a process.

• Nowadays, the --log-file parameter is deprecated for Kubernetes components and should not be used anymore. kube-log-runner is a direct replacement.

For example instead of running kube-apiserver like this:

"/bin/sh",
  "-c",
  "exec kube-apiserver {{params}} --allow-privileged={{pillar['allow_privileged']}} 1>>/var/log/kube-apiserver.log 2>&1"

Or this:

kube-apiserver {{params}} --allow-privileged={{pillar['allow_privileged']}} --log-file=/var/log/kube-apiserver.log --alsologtostderr=false"

We would use kube-log-runner like so:

kube-log-runner -log-file=/var/log/kube-apiserver.log --also-stdout=false \
   kube-apiserver {{params}} --allow-privileged={{pillar['allow_privileged']}}

The kube-log-runner then ensures that we run the /usr/local/bin/kube-apiserver with the specified parameters and redirect both stdout and stderr ONLY to the log file specified. It will always append to the log file.

Possible invocations:

# Merge stderr and stdout, write to stdout (same as 2>&1).
kube-log-runner echo "hello world"

# Redirect both into log file (same as 1>>/tmp/log 2>&1).
kube-log-runner -log-file=/tmp/log echo "hello world"

# Copy into log file and print to stdout (same as 2>&1 | tee -a /tmp/log).
kube-log-runner -log-file=/tmp/log -also-stdout echo "hello world"

# Redirect only stdout into log file (same as 1>>/tmp/log).
kube-log-runner -log-file=/tmp/log -redirect-stderr=false echo "hello world"

Container base image

The Kubernetes registry.k8s.io/build-image/go-runner image wraps the gcr.io/distroless/static image and provides kube-log-runner under its traditional name as /go-runner. It gets maintained in https://github.com/kubernetes/release/tree/master/images/build/go-runner.

Prebuilt binary

The Kubernetes release archives contain kube-log-runner.