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Add instructions on setting MaxScale passive/active to Keepalived tutorial

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Esa Korhonen
2018-02-14 15:03:03 +02:00
parent 3c153291f2
commit 13dea56c2d
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Documentation/Tutorials/Failover-with-Keepalived.md
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@ -188,3 +188,68 @@ Aug 11 10:51:57 maxscale2 Keepalived_vrrp[20257]: VRRP_Instance(VI_1) Entering F
Aug 11 10:51:57 maxscale2 Keepalived_vrrp[20257]: VRRP_Instance(VI_1) removing protocol VIPs.
Aug 11 10:51:57 maxscale2 Keepalived_vrrp[20257]: VRRP_Instance(VI_1) Now in FAULT state
```
## MaxScale active/passive-setting
When using multiple MaxScales with replication cluster management features
(failover, switchover, rejoin), only one MaxScale instance should be allowed to
modify the cluster at any given time. This instance should be the one with
MASTER Keepalived status. MaxScale itself does not know its state, but MaxCtrl
(a replacement for MaxAdmin) can set a MaxScale instance to passive mode. As of
version 2.2.2, a passive MaxScale behaves similar to an active one with the
distinction that it won't perform failover, switchover or rejoin. Even manual
versions of these commands will end in error. The passive/active mode
differences may be expanded in the future.
To have Keepalived modify the MaxScale operating mode, a notify script is
needed. This script is ran whenever Keepalived changes its state. The script
file is defined in the Keepalived configuration file as `notify`.
```
...
virtual_ipaddress {
192.168.1.13
}
track_script {
chk_myscript
}
notify /home/user/notify_script.sh
...
```
Keepalived calls the script with three parameters. In our case, only the third
parameter, STATE, is relevant. An example script is below.
```
#!/bin/bash
TYPE=$1
NAME=$2
STATE=$3
OUTFILE=/home/user/state.txt
case $STATE in
"MASTER") echo "Setting this MaxScale node to active mode" > $OUTFILE
maxctrl alter maxscale passive false
exit 0
;;
"BACKUP") echo "Setting this MaxScale node to passive mode" > $OUTFILE
maxctrl alter maxscale passive true
exit 0
;;
"FAULT") echo "MaxScale failed the status check." > $OUTFILE
maxctrl alter maxscale passive true
exit 0
;;
*) echo "Unknown state" > $OUTFILE
exit 1
;;
esac
```
The script logs the current state to a text file and sets the operating mode of
MaxScale. The FAULT case also attempts to set MaxScale to passive mode,
although the MaxCtrl command will likely fail.
If all MaxScale/Keepalived instances have a similar notify script, only one
MaxScale should ever be in active mode.