A small script to run as a sidecar container in order to create a quick updating ConfigMap. At least as on Kubernetes 1.11, updates to a ConfigMap can take an extended period of time to appear in pods.
While the community works on a built in solution (kubernetes/kubernetes#30189),
this sidecar is a workaround. It watches for all updates to a single ConfigMap,
and replicates changes to that ConfigMap into the directory /config. Create
an emptyDir volume mounted to /config in the sidecar, and then also mount
the volume (at any path) in the container that needs quick updating
configuration.
At runtime, two environment variables must be set:
NAMESPACE: the name of the current namespace that contains the ConfigMapCONFIG_MAP_NAME: the name of the ConfigMap to watch and replicate in the emptyDir volume
In addition, mount a volume to /config to capture the updated configuration.
The ServiceAccount running the sidecar must have read and watch access to
ConfigMaps in the namespace. For example, in OpenShift you can run oc adm policy add-role-to-user view -z default to give view access of all resources
to pods in the project.
apiVersion: v1
kind: Pod
metadata:
name: pseudoconfigmap-12-gjslv
namespace: cpitman-pseudoconfigmap
spec:
containers:
- env:
- name: CONFIG_MAP_NAME
value: test-config-map
- name: NAMESPACE
valueFrom:
fieldRef:
apiVersion: v1
fieldPath: metadata.namespace
image: ...
name: pseudoconfigmap
volumeMounts:
- mountPath: /config
name: config-volume
...
volumes:
- emptyDir: {}
name: config-volume
...