Configuring NiFi Registry Metadata Stores in Postgres

Postgres provides the option to use an externally located database that supports high availability.

Perform the following steps to use Postgres:

Download the Postgres JDBC driver and place it somewhere accessible to NiFi Registry
/path/to/drivers/postgresql-42.2.2.jar
Create a database inside Postgres
```
createdb nifireg
```

Create a database user and grant privileges.

psql nifireg
CREATE USER nifireg WITH PASSWORD 'changeme';
GRANT ALL PRIVILEGES ON DATABASE nifireg to nifireg;
\q

Configure the database properties in nifi-registry.properties.

nifi.registry.db.url=jdbc:postgresql://<POSTGRES-HOSTNAME>/nifireg
nifi.registry.db.driver.class=org.postgresql.Driver
nifi.registry.db.driver.directory=/path/to/drivers
nifi.registry.db.username=nifireg
nifi.registry.db.password=changeme