Support for multiple hosts

[vitaly-t]

PostgreSQL v10 was released on Oct 05, 2017, see the Release Notes.

---

One of the most interesting features that affects node-postgres is multiple host names or addresses in libpq connection strings and URIs.

This feature allows automatic support for replicas through the connection string, i.e. the first connection is tried, and if fails - the next one, and so on.

From documentation:

It is possible to specify multiple hosts to connect to, so that they are tried in the given order. In the Keyword/Value format, the host, hostaddr, and port options accept a comma-separated list of values. The same number of elements must be given in each option, such that e.g. the first hostaddr corresponds to the first host name, the second hostaddr corresponds to the second host name, and so forth. As an exception, if only one port is specified, it applies to all the hosts.

It may require some work within the driver to support it, but it will be very much worthwhile 😉

[vitaly-t]

Renamed the title again, because the connection attempts as such are out of the scope, libpq should handle it. This library only needs to support the new syntax for the connection strings, and perhaps update some connection logic internally.

[charmander]

@vitaly-t Isn’t this something the pure-JS library should have feature parity with?

[vitaly-t]

I believe it should, yes.

[vitaly-t]

Notation that the connection string should support: https://github.com/mongodb/specifications/blob/master/source/connection-string/connection-string-spec.rst

And then the driver needs to be extended accordingly.

[saule1508]

This would be super useful, the connection string is also described here http://paquier.xyz/postgresql-2/postgres-10-libpq-read-write/ and here https://www.postgresql.org/docs/10/static/libpq-connect.html

A typical use case would be where repmgrd would take care of the automatic failover and the client would automatically reconnect to the new primary when a failover did occur

I tried this but it is not working (primary and standby are running in docker containers on local host)

const { Pool } = require('pg');
const url = 'postgresql://repmgr:rep123@127.0.0.1:15432,127.0.0.1:25432/repmgr?target_session_attrs=read-write';

const pool = new Pool({
  connectionString:  url
})

[vitaly-t]

Just a health check, since this was open 6 month ago... Any attempt at implementing this yet?

[vitaly-t]

Generic connection-string is now available, which supports the full multi-host notation. This library should be used in place of the current connection string parser.

[denchistyakov]

Good day, have you plans to fix this issue and move to connection-string module?