The purpose of this document is to present the design decision behind Kuryr Kubernetes Health Managers.
The main purpose of the Health Managers is to perform Health verifications that assures readiness and liveness to Kuryr Controller and CNI pod, and so improve the management that Kubernetes does on Kuryr-Kubernetes pods.
Kuryr Controller might get to a broken state due to problems like: unable to connect with services it depends on and they being not healthy.
It is important to check health of these services so that Kubernetes and its users know when Kuryr Controller is ready to perform its networking tasks. Also, it is necessary to check the health state of Kuryr components in order to assure Kuryr Controller service is alive. To provide these functionalities, Controller's Health Manager will verify and serve the health state of these services and components to the probes.
Besides these problems on the Controller, Kuryr CNI daemon also might get to a broken state as a result of its components being not healthy and necessary configurations not present. It is essential that CNI components health and configurations are properly verified to assure CNI daemon is in a good shape. On this way, the CNI Health Manager will check and serve the health state to Kubernetes readiness and liveness probes.
One of the endpoints provided by the Controller Health Manager will check whether it is able to watch the Kubernetes API, authenticate with Keystone and talk to Neutron, since these are services needed by Kuryr Controller. These checks will assure the Controller readiness. The other endpoint, will verify the health state of Kuryr components and guarantee Controller liveness.
The CNI Health Manager also provides two endpoints to Kubernetes probes. The endpoint that provides readiness state to the probe checks connection to Kubernetes API and presence of NET_ADMIN capabilities. The other endpoint, which provides liveness, validates whether IPDB is in working order, maximum CNI ADD failure is reached, health of CNI components and existence of memory leak.
The CNI Health Manager will be started with the check for memory leak disabled. In order to enable, set the following option in kuryr.conf to a limit value of memory in MiBs.
[cni_health_server] max_memory_usage = -1
The CNI Health Manager is added as a process to CNI daemon and communicates to the other two processes i.e. Watcher and Server with a shared boolean object, which indicates the current health state of each component.
The idea behind these two Managers is to combine all the necessary checks in servers running inside Kuryr Controller and CNI pods to provide the result of these checks to the probes.