This sidecar is an individual Testground process responsible for network management and traffic shaping for test plan instances. It runs in privileged-mode on host machines, and listens for requests from test plan instances for network configuration through the sync service.

The sidecar is one of the three processes in the Testground executable. The other two are the Testground daemon and the Testground client. It can be started with:

$ testground sidecar --runner local:docker # or cluster:k8s

The sidecar runs in Docker and Kubernetes environments (i.e. when using the local:docker or the cluster:k8srunners). For now it is not supported and it does not run when using the local:exec runner.

On Kubernetes, each worker node runs the sidecar. We schedule it via a DaemonSet.

Usually, you will never need to start the sidecar manually. Each runner's health checks (which run prior to a test run) will ensure that the sidecar is running.

Responsibilities

Sidecars are responsible for three things:

1. Initializing the network interfaces of test instances. See Networking for more info.

   • Sidecars watch the local Docker daemon for containers being started and stopped.

   • For each new container, they adjust the routing of the control network, and they initialize the data network, incrementing the network-initialized state on the sync service every time a new test plan container is instrumented under a given run_id.

2. Applying networking configurations requested by test plan instances, by targeting the appropriate data interface through Netlink. See Networking for more info.

3. Periodically garbage-collect inactive entries in the sync service (backed by a Redis database), pertaining to finished runs.