Here's the approach in a nutshell:

• forward the stdout of the main application container to a file
• run a sidecar container and share the file where the main application container writes the logs
• run a filtering process in the sidecar that continuously reads the main application log file and writes the filtered logs to the sidecar stdout
• collect the sidecar stdout as the application logs

This approach allows us to filter the logs for a single application in the cluster, and assumes the main application can be modified to output its stdout to a file.

In the sample directory there is a simple NodeJS application and the Kubernetes manifests to deploy the main application and the filter.

Prerequisites:

• the Go toolchain
• glide
• make (optional)

To build from source:

• glide install
• make build or go build to build the binary for your OS
• if running and testing locally, you must specify a local LOGS_FILE, the location of your Kubernetes config file through KUBECONFIG and the desired namespace to filter secrets from through KUBECONFIG.