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lepe
Asked: 2017-05-14 22:02:18 +0800 CST

LXD + Galera Cluster + Max Scale : Shutting down server != Stopping containers

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I have a galera cluster with 4 nodes. 2 in one server (server-master) and 2 in another server (server-slave).

The clusters are controlled through "Max Scale".

All the setup seems correct as replication is working fine, SHOW STATUS LIKE 'wsrep_cluster_size' reports correct size in all nodes, shutting the master is successfully transfered to the next node, etc.

maxscale server status reports: (summarized for simplicity)

Master, Synced, Running | Slave, Synced, Running | Slave, Synced, Running

If I execute stop both containers at the same time in "server-master", master DB is successfully assigned to the first container in "slave".

maxscale server status reports:

Down | Down | Master, Synced, Running | Slave, Synced, Running

The problem is: if I shutdown server-master,

maxscale server status reports:

Down, Down, Running, Running

And trying to connect to the cluster results in connection failed. After sometime, all nodes are reported Down.

I don't understand why shutting down the server doesn't work as expected.

UPDATE

I discovered that if I turn off the second node in "server-master", and then I shutdown the server,"master" is successfully assigned to "server-slave", however after few minutes all nodes go down. :/

Servers: Ubuntu Servers 16.04 x64
MaxScale version: 2.0.5
LXD version: 2.13
Galera version (3): 25.3.20-xenial
Guide followed: https://www.digitalocean.com/community/tutorials/how-to-configure-a-galera-cluster-with-mariadb-10-1-on-ubuntu-16-04-servers
ubuntu

1 Answers

  1. Best Answer

    it's related to galera cluster behaviour.

    • You shutdown mysql in 1 node, before shutting down mysql in the node send leave request and leave the cluster gracefully. Your cluster detect that 2 nodes are leave and still can work with 2 nodes.
    • You shutdown host, mysql is killed and of course can not send leave request. Cluster detect that 2 nodes are dead and it has only 2 nodes left that <= 50% total number of cluster size. Cluster is put it fail state and can not accept connection.

    So, you can not connect from client to maxscale ---> cluster.

    ref : http://galeracluster.com/documentation-webpages/weightedquorum.html

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