======
repmgr
======

Installation Steps
==================

To install repmgr and repmgrd follow these steps:

1. Build repmgr programs 

2. Check your primary server is correctly configured

3. Write a suitable repmgr.conf for the node

4. Set up trusted copy between postgres accounts (this is only useful for 
   the ``STANDBY CLONE`` case)

5. repmgrd additional steps

Build repmgr programs
---------------------

Both methods of installation will place the binaries at the same location as your
postgres binaries, such as ``psql``.  There are two ways to build it.  The second
requires a full PostgreSQL source code tree to install the program directly into.
The first instead uses the PostgreSQL Extension System (PGXS) to install.  For
this method to work, you will need the pg_config program available in your PATH.
In some distributions of PostgreSQL, this requires installing a separate
development package in addition to the basic server software.  For example, 
the RPM packages of PostgreSQL put ``pg_config`` into the ``postgresql-devel``
package, not the main server one.

Build repmgr programs - PGXS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you are using a packaged PostgreSQL build and have ``pg_config``
available, the package can be built and installed using PGXS instead::

  tar xvzf repmgr-1.0.tar.gz
  cd repmgr
  make USE_PGXS=1
  make USE_PGXS=1 install

This is preferred to building from the ``contrib`` subdirectory of the main
source code tree.

If you need to remove the source code temporary files from this directory,
that can be done like this::

  make USE_PGXS=1 clean

Using a full source code tree
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In this method, the repmgr distribution is copied into the PostgreSQL source
code tree, assumed to be at the ${postgresql_sources} for this example.
The resulting subdirectory must be named ``contrib/repmgr``, without any
version number::

  cp repmgr.tar.gz ${postgresql_sources}/contrib
  cd ${postgresql_sources}/contrib 
  tar xvzf repmgr-1.0.tar.gz
  cd repmgr
  make
  make install

If you need to remove the source code temporary files from this directory,
that can be done like this::

  make clean

Confirm software was built correctly
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You should now find the repmgr programs available in the subdirectory where
the rest of your PostgreSQL installation is at.  You can confirm the software
is available by checking its version::

  repmgr --version
  repmgrd --version
    
Note that if you have a RPM install of PostgreSQL 9.0, the entire PostgreSQL
binary directory will not be in your PATH by default.  You may need to include
the full path of the binary instead, such as::

  /usr/pgsql-9.0/bin/repmgr --version
  /usr/pgsql-9.0/bin/repmgr --version

Check your primary server configuration
---------------------------------------

PostgreSQL should have been previously built and installed on the system.  Here
is a sample of changes to the postgresql.conf file::

  listen_addresses='*'
  wal_level = 'hot_standby'
  archive_mode = on
  archive_command = 'cd .'	 # we can also use exit 0, anything that just do 
                             # nothing
  max_wal_senders = 10
  wal_keep_segments = 5000     # 80 GB required on pg_xlog
  hot_standby = on

Also you need to add the machines that will participate in the cluster in 
pg_hba.conf file.  One possibility is to trust all connections from the
replication users from all addresses, such as::

    host     repmgr           repmgr      10.8.0.0/24         trust
    host     replication      all         10.8.0.0/24         trust

It is preferred that you have a repmgr user and database and just give 
access to that user.  If you give a password to the user, you need to create
a .pgpass file for them as well to allow automatic login.

Write a suitable repmgr.conf
----------------------------

It should have these three parameters:

1. cluster: A string (single quoted) that identify the cluster we are on 

2. node: An integer that identify our node in the cluster

3. conninfo: A string (single quoted) that teach repmgr how to connect to this node

Set up trusted copy between postgres accounts
---------------------------------------------

Initial copy between nodes uses the rsync program running over ssh.  For this 
to work, the postgres accounts on each system need to be able to access files 
on their partner node without a password.

First generate a ssh key, using an empty passphrase, and copy the resulting 
keys and a maching authorization file to a privledged user on the other system::

  [postgres@db1]$ ssh-keygen -t rsa
  Generating public/private rsa key pair.
  Enter file in which to save the key (/var/lib/pgsql/.ssh/id_rsa): 
  Enter passphrase (empty for no passphrase): 
  Enter same passphrase again: 
  Your identification has been saved in /var/lib/pgsql/.ssh/id_rsa.
  Your public key has been saved in /var/lib/pgsql/.ssh/id_rsa.pub.
  The key fingerprint is:
  aa:bb:cc:dd:ee:ff:aa:11:22:33:44:55:66:77:88:99 postgres@db1.domain.com
  [postgres@db1]$ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
  [postgres@db1]$ chmod go-rwx ~/.ssh/*
  [postgres@db1]$ cd ~/.ssh
  [postgres@db1]$ scp id_rsa.pub id_rsa authorized_keys user@db2:

Login as that user on the other system, and install the files into the postgres 
user's account::

  [user@db2 ~]$ sudo chown postgres.postgres authorized_keys id_rsa.pub id_rsa
  [user@db2 ~]$ sudo mkdir -p ~postgres/.ssh
  [user@db2 ~]$ sudo chown postgres.postgres ~postgres/.ssh
  [user@db2 ~]$ sudo mv authorized_keys id_rsa.pub id_rsa ~postgres/.ssh
  [user@db2 ~]$ sudo chmod -R go-rwx ~postgres/.ssh

Now test that ssh in both directions works (you may have to accept some new 
known hosts in the process)

repmgrd additional steps
========================

To use the repmgrd (repmgr daemon) to monitor standby so we know how is going 
the replication and how far they are from primary, you need to execute the 
``repmgr.sql`` script in the postgres database.

You also need to add a row for every node in the repl_node table