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Shorten the introduction

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Sergey Dudoladov 2018-05-16 17:25:03 +02:00
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@ -4,27 +4,15 @@
[![Coverage Status](https://coveralls.io/repos/github/zalando-incubator/postgres-operator/badge.svg)](https://coveralls.io/github/zalando-incubator/postgres-operator)
[![Go Report Card](https://goreportcard.com/badge/github.com/zalando-incubator/postgres-operator)](https://goreportcard.com/report/github.com/zalando-incubator/postgres-operator)
The Postgres operator manages PostgreSQL clusters on Kubernetes using the [operator pattern](https://coreos.com/blog/introducing-operators.html).
During the initial run it registers the [Custom Resource Definition (CRD)](https://kubernetes.io/docs/concepts/api-extension/custom-resources/#customresourcedefinitions) for Postgres.
The `postgresql` CRD is essentially the schema that describes the contents of the manifests for deploying individual
Postgres clusters using StatefulSets and [Patroni](https://github.com/zalando/patroni).
## Introduction
Once the operator is running, it performs the following actions:
The Postgres [operator](https://coreos.com/blog/introducing-operators.html) manages PostgreSQL clusters on Kubernetes:
* watches for new `postgresql` manifests and deploys new clusters
* watches for updates to existing manifests and changes corresponding properties of the running clusters
* watches for deletes of the existing manifests and deletes corresponding clusters
* acts on an update to the operator configuration itself and changes the running clusters when necessary
(i.e. the Docker image changes for a minor release update)
* periodically checks running clusters against the manifests and syncs changes
1. The operator watches additions, updates and deletions of Postgresql manifests (cluster descriptions) and changes the running clusters accordingly. For example, when a user submits a new manifest, the operator fetches that object and spawns a new Postgres cluster, including all necessary entities such as Kubernetes StatefulSets and Postgres roles. The [`postgresql` Custom Resource Definition](https://kubernetes.io/docs/concepts/api-extension/custom-resources/#customresourcedefinitions) defines settings that a cluster manifest may contain (see example).
Example: When a user creates a new custom object of type ``postgresql`` by submitting a new manifest with
``kubectl``, the operator fetches that object and creates the required Kubernetes entities to spawn a new Postgres cluster
(StatefulSets, Services, Secrets).
2. The operator also watches updates to its own configuration and alters running Postgres clusters if necessary. For instance, if a pods' Docker image is changed, the operator carries out the rolling update. That is, it re-spawns one-by-one pods from each StatefulSet it manages with the new Docker image.
Update example: After changing the Docker image inside the operator's configuration, the operator first goes to all StatefulSets
it manages and updates them with the new Docker image; afterwards, all pods from each StatefulSet are killed one by one
and the replacements are spawned automatically by each StatefulSet with the new Docker image. This is called the Rolling update.
3. Finally, the operator periodically synchronizes the actual state of each Postgres cluster with the desired state defined in the cluster's manifest.
## Quickstart
@ -55,6 +43,7 @@ We have automated these steps for you:
```bash
cd postgres-operator
./run_operator_locally.sh
minikube delete
```
## Scope