Using sidecar containers¶
The Operator allows you to deploy additional (so-called sidecar) containers to the Pod. You can use this feature to run debugging tools, some specific monitoring solutions, etc.
Note
Custom sidecar containers can easily access other components of your cluster. Therefore they should be used carefully and by experienced users only.
Adding a sidecar container¶
You can add sidecar containers to Percona Distribution for MongoDB Replica Set,
Config Servers, and mongos Pods. Just use sidecars subsection in the
replsets, sharding.configsvrReplSet, and sharding.mongos of the
deploy/cr.yaml configuration file. In this subsection, you should specify
the name and image of your container and possibly a command to run:
spec:
replsets:
....
sidecars:
- image: busybox
command: ["/bin/sh"]
args: ["-c", "while true; do echo echo $(date -u) 'test' >> /dev/null; sleep 5; done"]
name: rs-sidecar-0
....
Apply your modifications as usual:
$ kubectl apply -f deploy/cr.yaml
Running kubectl describe command for the appropriate Pod can bring you the
information about the newly created container:
$ kubectl describe pod my-cluster-name-rs0-0
Expected output
....
Containers:
....
rs-sidecar-0:
Container ID: docker://f0c3437295d0ec819753c581aae174a0b8d062337f80897144eb8148249ba742
Image: busybox
Image ID: docker-pullable://busybox@sha256:139abcf41943b8bcd4bc5c42ee71ddc9402c7ad69ad9e177b0a9bc4541f14924
Port: <none>
Host Port: <none>
Command:
/bin/sh
Args:
-c
while true; do echo echo $(date -u) 'test' >> /dev/null; sleep 5; done
State: Running
Started: Thu, 11 Nov 2021 10:38:15 +0300
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-fbrbn (ro)
....
Getting shell access to a sidecar container¶
You can login to your sidecar container as follows:
$ kubectl exec -it my-cluster-name-rs0-0 -c rs-sidecar-0 -- sh
/ #
Mount volumes into sidecar containers¶
It is possible to mount volumes into sidecar containers.
Following subsections describe different volume types, which were tested with sidecar containers and are known to work.
Persistent Volume¶
You can use Persistent volumes when you need dynamically provisioned storage which doesn’t depend on the Pod lifecycle. To use such volume, you should claim durable storage with persistentVolumeClaim without specifying any non-important details.
The following example requests 1G storage with sidecar-volume-claim
PersistentVolumeClaim, and mounts the correspondent Persistent Volume to the
rs-sidecar-0 container’s filesystem under the /volume0 directory:
...
sidecars:
- image: busybox
command: ["/bin/sh"]
args: ["-c", "while true; do echo echo $(date -u) 'test' >> /dev/null; sleep 5; done"]
name: rs-sidecar-0
volumeMounts:
- mountPath: /volume0
name: sidecar-volume-claim
sidecarPVCs:
- apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: sidecar-volume-claim
spec:
resources:
requests:
storage: 1Gi
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
Note
Sidecar containers for mongos Pods have limited Persistent volumes
support: sharding.mongos.sidecarPVCs option can be used if there is a
single mongos in deployment or when ReadWriteMany/ReadOnlyMany
access modes are used (but these modes are available not in every storage).
Secret¶
You can use a secret volume to pass the information which needs additional protection (e.g. passwords), to the container. Secrets are stored with the Kubernetes API and mounted to the container as RAM-stored files.
You can mount a secret volume as follows:
...
sidecars:
- image: busybox
command: ["/bin/sh"]
args: ["-c", "while true; do echo echo $(date -u) 'test' >> /dev/null; sleep 5; done"]
name: rs-sidecar-0
volumeMounts:
- mountPath: /secret
name: sidecar-secret
sidecarVolumes:
- name: sidecar-secret
secret:
secretName: mysecret
The above example creates a sidecar-secret volume (based on already existing
mysecret Secret object)
and mounts it to the rs-sidecar-0 container’s filesystem under the
/secret directory.
Note
Don’t forget you need to create a Secret Object before you can use it.
configMap¶
You can use a configMap volume to pass some configuration data to the container. Secrets are stored with the Kubernetes API and mounted to the container as RAM-stored files.
You can mount a configMap volume as follows:
...
sidecars:
- image: busybox
command: ["/bin/sh"]
args: ["-c", "while true; do echo echo $(date -u) 'test' >> /dev/null; sleep 5; done"]
name: rs-sidecar-0
volumeMounts:
- mountPath: /config
name: sidecar-config
sidecarVolumes:
- name: sidecar-config
configMap:
name: myconfigmap
The above example creates a sidecar-config volume (based on already existing
myconfigmap configMap object)
and mounts it to the rs-sidecar-0 container’s filesystem under the /config
directory.
Note
Don’t forget you need to create a configMap Object before you can use it.
