Hi guys,
Few month ago, I started a new chapter about this exact subject for "PAF -
Cluster administration under CentOS" ( see:
https://clusterlabs.github.io/PAF/CentOS-7-admin-cookbook.html)
Please, find attach my draft.
All feedback, fix, comments and intensive tests are welcome!
## Adding IPs on slaves nodes
In this chapter, we are using a three node cluster with one PostgreSQL master
instance and two standbys instances.
As usual, we start from the cluster created in the quick start documentation:
* one master resource called `pgsql-ha`
* an IP address called `pgsql-master-ip` linked to the `pgsql-ha` master role
See the [Quick Start CentOS 7]({{ site.baseurl}}/Quick_Start-CentOS-7.html#cluster-resources)
for more informations.
We want to create two IP addresses with the following properties:
* start on a standby node
* avoid to start on the same standby node than the other one
* move to the available standby node should a failure occurs to the other one
* move to the master if there is no standby alive
To make this possible, we have to play with the resources co-location scores.
First, let's add two `IPaddr2` resources called `pgsql-ip-stby1` and
`pgsql-ip-stby2` holding IP addresses `192.168.122.49` and `192.168.122.48`:
~~~
# pcs resource create pgsql-ip-stby1 ocf:heartbeat:IPaddr2 \
cidr_netmask=24 ip=192.168.122.49 op monitor interval=10s \
# pcs resource create pgsql-ip-stby2 ocf:heartbeat:IPaddr2 \
cidr_netmask=24 ip=192.168.122.48 op monitor interval=10s \
~~~
We want both IP addresses to avoid co-locating with each other. We add
a co-location constraint so `pgsql-ip-stby2` avoids `pgsql-ip-stby1` with a
score of `-5`:
~~~
#Â pcs constraint colocation add pgsql-ip-stby2 with pgsql-ip-stby1 -5
~~~
> **NOTE**: that means the cluster manager have to start `pgsql-ip-stby1` first
> to decide where `pgsql-ip-stby2` should start according to the new scores in
> the cluster. Also, that means that whenever you move `pgsql-ip-stby1` to
> another node, the cluster might have to stop `pgsql-ip-stby2` first and
> restart it elsewhere depending on new scores.
{: .notice}
Now, we add similar co-location constraints to define that each IP address
prefers to run on a node with a slave of `pgsql-ha`:
~~~
# pcs constraint colocation add pgsql-ip-stby1 with slave pgsql-ha 10
# pcs constraint order start pgsql-ha then start pgsql-ip-stby1 kind=Mandatory
# pcs constraint colocation add pgsql-ip-stby2 with slave pgsql-ha 10
# pcs constraint order start pgsql-ha then start pgsql-ip-stby2 kind=Mandatory
~~~
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