Document stategic merge patch. (prometheus-operator#3823)

* stategic merge patch * Apply suggestions from code review Optimize doc words Co-authored-by: Lili Cosic <[email protected]> * Apply suggestions from code review Co-authored-by: Simon Pasquier <[email protected]> * remove endline * add endline Co-authored-by: Lili Cosic <[email protected]> Co-authored-by: Simon Pasquier <[email protected]>
petersin0422 · Feb 9, 2021 · 91cf69f · 91cf69f
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+# Strategic merge patch
+
+When users need to apply a specific configuration to containers that we do not support or do not currently exist, merge patch can be used.
+This document describes how to overwrite the container configuration generated by the operator by merging patches.
+
+## How the "strategic merge patch" works
+
+The operator supports `containers` field in `PrometheusSpec`, `AlertmanagerSpec` and `ThanosRulerSpec` configuration.
+This field allows injecting additional containers, and the existing configuration can be overwritten by sharing the same container name.
+
+### Merge patch example of Prometheus
+
+The following manifest overwrites the `failureThreshold` value of the readiness probe for the Prometheus container.
+
+```
+apiVersion: monitoring.coreos.com/v1
+kind: Prometheus
+metadata:
+  labels:
+    prometheus: self
+  name: self
+  namespace: default
+spec:
+  containers:
+  - name: prometheus
+    readinessProbe:
+      failureThreshold: 500
+```
+
+### Merge patch example for Alertmanager
+
+The following manifest overwrites the `failureThreshold` values of the readiness and liveness probes for the Alertmanager container.
+
+```
+apiVersion: monitoring.coreos.com/v1
+kind: Alertmanager
+metadata:
+  labels:
+    alertmanager: main
+  name: main
+  namespace: monitoring
+spec:
+  containers:
+  - name: alertmanager
+    livenessProbe:
+      failureThreshold: 5
+    readinessProbe:
+      failureThreshold: 5
+```