Examining Cluster Metrics

oc adm

oc adm top pods -A --sum

oc adm must-gather --dest-dir /home/student/must-gather

oc adm inspect clusteroperator/openshift-apiserver \
clusteroperator/kube-apiserver


oc adm inspect clusteroperator/openshift-apiserver --since 10m

oc adm top pods -A --sum

oc adm top pods etcd-master01 -n openshift-etcd --containers

Query Cluster Events and Alerts

oc debug

oc debug job/test --as-user=10000

oc debug node/node-name

Run Applications as Containers and Pods

oc run RESOURCE/NAME --image IMAGE [options]

kubectl run web-server --image registry.access.redhat.com/ubi8/httpd-24

# -- arguments
kubectl run RESOURCE/NAME --image IMAGE -- arg1 arg2 ... argN

oc exec RESOURCE/NAME -- COMMAND [args...] [options]

oc exec my-app -- date # exec in the first container of the pod
kubectl exec my-app -c ruby-container -- date
oc attach my-app -it

Node debug

ssh to a node or

create a debug pod

oc debug node/node-name
chroot /host

cri debug

# get pod id
crictl pods --name master01-debug

# get container name from pod id
crictl ps -p cb066ee76b598 -o json | jq -r .containers[0].metadata.name

# get container id
CID=$(crictl ps --name container-00 -o json | jq -r .containers[0].id)

# get PID of the container
crictl inspect $CID | grep pid

# list namespaces

lsns -p pid

# enter the container namespace
nsenter -t PID -p -r ps -ef
# -t PID - target PID
# -p - enter PID namespace
# -r -  set the top-level directory

Common Resource Types

Templates

Templates (RHOCP feature) - a yaml manifest that contains parameterized definitions of one or more resources. Processed by the oc process command, which replaces value and generates resource definitions. The resulting resource definitions can be applied to a cluster using the oc apply command.

# process and generate resource definitions from a file.
oc process -f mysql-template.yaml -o yaml

# display the parameters defined in a template
oc process -f mysql-template.yaml --parameters

You also use templates with the oc new-app command

oc new-app --template=mysql-persistent

Pod

the smallest compute unit that can be defined.

DeploymentConfig

Deployment configurations define the specification of a pod. They manage pods by creating replication controllers.

Deployment

Similar to deployment configurations, deployments define the intended state of a replica set.

ReplicaSet

Replica sets define a configurable number of pods that match a specification.

Project

A project is a Kubernetes namespace with additional annotations, and is the primary method for managing access to resources in a cluster.

Service

an object for internal pod-to-pod communication. Application send requests to a service and and port.