The right way of starting up a Galera Cluster

Question

I am confused about the bootstrap process of MariaDB Galera Cluster.

Let's say we have 3 nodes of a MariaDB Galera Cluster, working and functioning normally on CentOS6/7. However, at some point we have (doesn't matter by what reason) to stop all 3 nodes and then start up the cluster. We are stopping the nodes 1 by 1 normally and cleanly. In order to start up the cluster, I go and check out grastate.dat and see which node is with most current data. I bootstrap this node first.

What is unclear to me is how the bootstrap is done exactly for CentOS 6 and 7. The 2nd and 3rd node can be started with systemctl start mysql. How do we start the first node? Do we use service mysql start --bootstrap on the first node with most current data? I read that for CentOS 7 it's systemctl start [email protected]. What is the procedure of boostrapping the first node of the cluster after we stopped all 3 nodes normally?

PS: Related to this, with some more details, is the post by dr01: grastate.dat with seqno -1 on a healthy cluster. Why?

Roman Bogachev · Accepted Answer · 2016-03-30 12:50:23Z

At MariaDB 10.1 where Galera included you need to start first node with key --wsrep-new-cluster

e.g. /etc/init.d/mysql start --wsrep-new-cluster

All other nodes starts as usually:

/etc/init.d/mysql start

To determine which node needs to be bootstrapped, compare the wsrep_last_committed value on all DB nodes:

KVM-1> SHOW STATUS LIKE 'wsrep_%'; +----------------------+-------------+ | Variable_name | Value | +----------------------+-------------+ | wsrep_last_committed | 21568 | ... | wsrep_cluster_status | non-Primary | +----------------------+-------------+ KVM-2> SHOW STATUS LIKE 'wsrep_%'; +----------------------+-------------+ | Variable_name | Value | +----------------------+-------------+ | wsrep_last_committed | 1359 | ... | wsrep_cluster_status | non-Primary | +----------------------+-------------+ KVM-3> SHOW STATUS LIKE 'wsrep_%'; +----------------------+-------------+ | Variable_name | Value | +----------------------+-------------+ | wsrep_last_committed | 537 | ... | wsrep_cluster_status | non-Primary | +----------------------+-------------+

KVM-1 has the most up-to-date data. In this case, all Galera nodes are already started, so you don’t necessarily need to bootstrap the cluster again. We just need to promote KVM-1 to be a Primary Component:

KVM-1> SET GLOBAL wsrep_provider_options="pc.bootstrap=1";

The remaining nodes will then reconnect to the Primary Component (KVM-1) and resyncing back data based on this node.

Roman, first thank you for your reply. But with --wsrep-new-cluster it will create a new cluster right? Is this the normal behavior - to create a new cluster if all nodes were stopped and then started? Will this reflect somehow on the databases/schemas and data? — user3526540
– user3526540, Commented Mar 30, 2016 at 12:26
Which replication do you use: Master-Slave or Master-Master? This newer bootstrapping method was enabled by the --wsrep-new-cluster command-line option. MariaDB Docs. As for me, I use 3 nodes with master-master replication, and when all of the nodes are down, I starts one of the stable nodes with this key and other nodes as usual. — Roman Bogachev
– Roman Bogachev, Commented Mar 30, 2016 at 12:32
Master-Master, 3 nodes. I am just confused if by any chance I stopped normally the 3 nodes, how to boot the primary one (I'll identified that from the seq found in grastate.dat). Is it fine to create a new cluster when I have all 3 nodes stopped? Because --wsrep-new-cluster will do exactly this. Will I lose or messed the data/schemas of the old cluster? — user3526540
– user3526540, Commented Mar 30, 2016 at 12:34
I use 3 nodes with master-master too. dba.stackexchange.com/questions/133668/galera-wont-start/… — Roman Bogachev
– Roman Bogachev, Commented Mar 30, 2016 at 12:38
Did you stop all nodes in your case or that was the first initial run of the cluster? In my case I have wsrep_cluster_address="gcomm://node1,node2,node3" in all 3 nodes. I don't get again the start up procedure. — user3526540
– user3526540, Commented Mar 30, 2016 at 12:50

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