The following items are new for Chef server 12.16.2:

- **Upgrade to PostgreSQL 9.6**
- **Elasticsearch 5 support**
- **Changes to Erlang Port Mapper Daemon (EPMD) listening ports**
- **RabbitMQ health check in status endpoint**
- **Notification of affected services when updating secrets with set-secret**

## Upgrade to PostgreSQL 9.6

Chef server now uses the latest stable version of the 9.6 series
(9.6.3). Upgrades of existing installations are done automatically, but
creating backups is advised.

The information below only applies if you have set a custom value set
for `checkpoint_segments` in your `/etc/opscode/chef-server.rb`. If you
have not set a custom value, there is nothing to change:

The `checkpoint_segments` configuration setting is gone, so if you
previously used the following parameter:

```ruby
postgresql['checkpoint_segments'] = 10
```

You would instead use:

```ruby
postgresql['max_wal_size'] = '3G'
```

This is just an example configuration - see the [PostgreSQL release
notes](https://www.postgresql.org/docs/9.6/static/release-9-5.html) for
more information on tuning this option. The default setting for
`max_wal_size` is `1G`. The PostgreSQL release notes mention a
conversion rule: `max_wal_size = (3 * checkpoint_segments) * 16MB`. They
also state that the default value for `max_wal_size` (1GB) should be
sufficient in most settings, so this conversion is not performed
automatically.

The `shmmax` and `shmall` configuration settings are no longer used, as
PostgreSQL 9.6 relies on System V shared memory much less than
PostgreSQL 9.2. The `shared_buffers` configuration setting is still
respected, and can be used to modify the amount of shared memory used by
PostgreSQL.

This update also adds two new configurables in the "Checkpoints" group:
`min_wal_size` and `checkpoint_flush_after`.

As part of the upgrade procedure, `chef-server-ctl cleanup` will remove
Postgres 9.2's data and logs.

## Elasticsearch 5 support

Chef server now supports Elasticsearch 5. This allows Chef server and
Chef Automate 1.6 to use the same Elasticsearch instance.

## Changes to EPMD listening ports

The Erlang Port Mapper Daemon (EPMD) included in version 12.16 is
patched to only listen on the addresses specified in `ERL_EPMD_ADDRESS`.
Before, it would implicitly add `::1` and `127.0.0.1` to the set of
listening addresses, which caused trouble for systems without `::1`.

## RabbitMQ health check in status endpoint

Chef server's `_status` endpoint now checks the health of the analytics
and internal RabbitMQ vhosts. For these checks to work, the RabbitMQ
management plugin must be installed. If it is not, the checks are not
performed. If Chef server is configured not to use Actions, a check will
not be performed against the Actions vhost. If an indexing queue is not
used, the `chef_index` RabbitMQ vhost will not be checked.

## Notification of affected services when updating secrets with set-secret

`chef-server-ctl set-secret` will notify the user of services that
depend on the secret that is being changed. When used with the optional
`--with-restart` flag, `chef-server-ctl set-secret` will attempt to
automatically restart the dependent services.