Configuring PID limits
A process identifier (PID) is a unique identifier assigned by the Linux kernel to each process or thread currently running on a system. The number of processes that can run simultaneously on a system is limited to 4,194,304 by the Linux kernel. This number might also be affected by limited access to other system resources such as memory, CPU, and disk space.
In OpenShift Container Platform 4.11 and later, by default, a pod can have a maximum of 4,096 PIDs. If your workload requires more than that, you can increase the allowed maximum number of PIDs by configuring a KubeletConfig object.
OpenShift Container Platform clusters running versions earlier than 4.11 use a default PID limit of 1024.
Understanding process ID limits
In OpenShift Container Platform, consider these two supported limits for process ID (PID) usage before you schedule work on your cluster:
-
Maximum number of PIDs per pod.
The default value is 4,096 in OpenShift Container Platform 4.11 and later. This value is controlled by the
podPidsLimitparameter set on the node.
When a pod exceeds the allowed maximum number of PIDs per pod, the pod might stop functioning correctly and might be evicted from the node. See the Kubernetes documentation for eviction signals and thresholds for more information.
When a node exceeds the allowed maximum number of PIDs per node, the node can become unstable because new processes cannot have PIDs assigned. If existing processes cannot complete without creating additional processes, the entire node can become unusable and require reboot. This situation can result in data loss, depending on the processes and applications being run. Customer administrators and Red Hat Site Reliability Engineering are notified when this threshold is reached, and a Worker node is experiencing PIDPressure warning will appear in the cluster logs.
Risks of setting higher process ID limits for OpenShift Container Platform pods
The podPidsLimit parameter for a pod controls the maximum number of processes and threads that can run simultaneously in that pod.
You can increase the value for podPidsLimit from the default of 4,096 to a maximum of 16,384. Changing this value might incur downtime for applications, because changing the podPidsLimit requires rebooting the affected node.
If you are running a large number of pods per node, and you have a high podPidsLimit value on your nodes, you risk exceeding the PID maximum for the node.
To find the maximum number of pods that you can run simultaneously on a single node without exceeding the PID maximum for the node, divide 3,650,000 by your podPidsLimit value. For example, if your podPidsLimit value is 16,384, and you expect the pods to use close to that number of process IDs, you can safely run 222 pods on a single node.