replication wip

storage/databases/postgres/3-replication/README.md

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+# How to replicate PostgreSQL
+
+So far we've learnt how to run PostgreSQL as per [chapter 1](../1-introduction/README.md). </br>
+We've also learnt how to configure PostgreSQL with our custom configuration file as per [chapter 2](../2-configuration/README.md). </br>
+
+In this chapter we will setup a second PostgreSQL instance. </br>
+Then we will learn how to configure our first PostgreSQL instance to replicate its data to the new second instance. </br>
+This will essentially give us a primary and a secondary server for better availability in case we lose our primary server. </br>
+
+
+* Documentation on HA \ replication \ failover modes
+
+
+## Get our Primary PostgreSQL up and running
+
+Let's start by running our PostgreSQL in docker </br>
+
+Few things to note here: </br>
+* We start our instance with a different name to identify it as the first instance with the `--name postgres-1` flag and `2` for the second instance
+* Set unique data volumes for data between instances
+* Set unique config files for each instance
+* Create and run our docker containers on the same network 
+
+Create a new network so our instances can talk with each other:
+
+```
+docker network create postgres
+```
+
+Start with instance 1: 
+
+```
+cd storage/databases/postgres/3-replication
+
+docker run -it --rm --name postgres-1 `
+--net postgres `
+-e POSTGRES_USER=postgresadmin `
+-e POSTGRES_PASSWORD=admin123 `
+-e POSTGRES_DB=postgresdb `
+-e PGDATA="/data" `
+-v ${PWD}/postgres-1/pgdata:/data `
+-v ${PWD}/postgres-1/config:/config `
+-p 5000:5432 `
+postgres:15.0 -c 'config_file=/config/postgresql.conf'
+```
+
+Start instance 2:
+
+```
+cd storage/databases/postgres/3-replication
+
+docker run -it --rm --name postgres-2 `
+--net postgres `
+-e POSTGRES_USER=postgresadmin `
+-e POSTGRES_PASSWORD=admin123 `
+-e POSTGRES_DB=postgresdb `
+-e PGDATA="/data" `
+-v ${PWD}/postgres-2/pgdata:/data `
+-v ${PWD}/postgres-2/config:/config `
+-p 5000:5432 `
+postgres:15.0 -c 'config_file=/config/postgresql.conf'
+```