Pass postgres parameter into Kubernetes deployment - postgresql

Question

I am trying to set a postgres parameter (shared_buffers) into my postgres database pod. I am trying to set an init container to set the db variable, but it is not working because the init container runs as the root user.
What is the best way to edit the db variable on the pods? I do not have the ability to make the change within the image, because the variable needs to be different for different instances. If it helps, the command I need to run is a "postgres -c" command.
"root" execution of the PostgreSQL server is not permitted.
The server must be started under an unprivileged user ID to prevent
possible system security compromise. See the documentation for
more information on how to properly start the server.

Answer 1

You didn't share your Pod/Deployment definition, but I believe you want to set shared_buffers from the command line of the actual container (not the init container) in your Pod definition. Something like this if you are using a deployment:
apiVersion: v1
kind: Deployment
metadata:
name: postgres
spec:
replicas: 1
template:
metadata:
labels:
app: postgres
spec:
containers:
- name: postgres
image: postgres:12.2
imagePullPolicy: "IfNotPresent"
command: ["postgres"] # <-- add this
args: ["-D", "-c", "shared_buffers=128MB"] # <-- add this
ports:
- containerPort: 5432
securityContext:
runAsUser: 1000
runAsGroup: 1000
fsGroup: 1000
volumeMounts:
- mountPath: /var/lib/postgresql/data
name: postgredb
- name: postgresql-config-volume # <-- use if you are using a ConfigMap (see below)
mountPath: /var/lib/postgres/data/postgresql.conf
volumes:
- name: postgredb
persistentVolumeClaim:
claimName: postgres-pv-claim # <-- note: you need to have this already predefined
- name: postgresql-config-volume # <-- use if you are using a ConfigMap (see below)
configMap:
name: postgresql-config
Notice that if you are using a ConfigMap you can also do this (note that you may want to add more configuration options besides shared_buffers):
apiVersion: v1
kind: ConfigMap
metadata:
name: postgresql-config
data:
postgresql.conf: |
shared_buffers=256MB

Answer 2

In my case, the #Rico answer didn't help me out of the box because I don't use postgres with a persistent storage mount, which means there is no /var/lib/postgresql/data folder and pre-existed database (so both proposed options have failed in my case).
To successfully apply postgres settings, I used only args (without command section).
In that case, k8s will pass these args to the default entrypoint defined in the docker image (docs), and as for postgres entrypoint, it is made so that any options passed to the docker command will be passed along to the postgres server daemon (look section Database Configuration at: https://hub.docker.com/_/postgres)
apiVersion: v1
kind: Pod
metadata:
name: postgres
spec:
containers:
- image: postgres:9.6.8
name: postgres
args: ["-c", "shared_buffers=256MB", "-c", "max_connections=207"]
To check that the settings applied:
$ kubectl exec -it postgres -- bash
root#postgres:/# su postgres
$ psql -c 'show max_connections;'
max_connections
-----------------
207
(1 row)