I am looking at creating a high availability Wordpress installation across two servers with a load balancer to distribute the traffic between these servers, I intend to setup a LAMP stack on these two web servers and configure MySQL master master replication to ensure both servers have the same content similar to the setup at https://www.linode.com/docs/websites/cms/high-availability-wordpress
For anyone created a similar setup before, is there anything to watch out for? Will this work without there being differences in the database assuming both nodes are online? If one node goes down will this synchronise with the other master node successfully?
This is a pretty old post, but I've set up exactly this recently.
I do not recommend setting up WordPress with master-master replication. The nodes went out of sync multiple times and resulted in split-brain. We've reverted back to master-slave replication because of the instability of the setup.
I recently tried this and regret it. I realize your post is now almost 2 years old, but thought I should put in my 2 cents for anyone considering this approach. I recommend you go with MariaDB with MaxScale to separate the reads and writes, and go with master-slave configuration. I'm running into all sorts of deadlocks, and issues with this configuration. Currently using MariaDB with Galera, with HAProxy up front.
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Please forgive my ignorance but I do not have a ton of experience with MySQL. I am a web developer but overall I have pretty much just installed MySQL or spun up an RDS instance, connected to it and everything just works. However I am currently being tasked with creating a complete backup of our primary server (essentially high availability with a load balancer etc). So I thought now might be a good time to change how I haver our MySQL setup to take advantage of having 2 servers. Currently our MySQL lives on our primary servers and that will probably stay that way for now, however my goal with this new setup is to have 2 identical servers, both running the application and both having the exact same MySQL data structure / data. I want to be able to essentially open up the web application on one server, make a change, see it on the other or vica versa.
From my research it looks like what I want is called "Master-Master Replication" however it seems as if this is an older / more outdated approach? Every article I read is from ~2010-2012 and most people say it is depreciated and I should use Percona XtraDB Cluster, MySQL Group Replication, or Galera Cluster etc. I basically have no idea what any of that means and I am looking for the easiest way to get Master-Master type setup working. On top of that even if I wanted to use regular Master-Master replication it seems as if this is something specific to MySQL and not Percona which is what I actually use.
I know plenty about dev ops and can get everything but the MySQL up and running in no time but I would love some insight on the best way to do this. Currently servers are running Centos 7, Percona 5.7, Apache 2.4.
The easiest way to start is to setup a percona xtradb cluster with proxysql.
Percona xtradb cluster handles all the problems that are present in basic MySQL Master-Master Replication.
Both Galera and Percona Xtradb CLuster are same, as they use the same galera plugin, Only that Percona has customized it and added some extra features like in built proxysql( kind of load balancer for database).
Let's clear up one thing first. Percona is MySQL. If a feature is available on Oracle MySQL (the community version is what I am referring to here), then it is also available on Percona. Think of the two like a cake: MySQL is the base "cake" and Percona is the frosting/sprinkles/etc that go on top.
That being said you can absolutely do Master/Master using Percona MySQL. The standard/best practice is to configure this in active/hot-standby. Meaning, do not write to both nodes at the same time. Your application, or your middleware/proxy, must isolate writes to only one node. This will save you insane headaches when/if replication breaks.
ProxySQL is not a Percona product, but we do support it 100%. You can place ProxySQL in front of your M/M and setup the correct query rules to only route to one MySQL.
You are correct that the most modern solution here, and in my opinion, an easier solution, is to set up a 3-node Percona XtraDB Cluster (PXC). Again, Galera MySQL is the "cake" and PXC is all the extras on top. Group Replication is pie (just to continue the analogy.)
We consider a 3-node PXC fronted with ProxySQL to be one of the best HA solutions out there for MySQL. It is still best practice to only write to one node, and utilize the other 2 for read-only queries. If the primary node goes down, each of the other two have an up-to-the-transaction copy of the data. Again, ProxySQL helps route the traffic if primary goes down.
Backups can be taken from any PXC node using Percona XtraBackup in a non-blocking/hot fashion.
We use mysql multi-source replication, analysts and developers works with the databases, it's a main task of server(cross-bases queries, etc). Mysql slave replicates data from about 10-15 servers, some of them is realy big (400gb, 500gb, 1.5tb). Slave host - ec2 r4.2xlarge. But have some problems, main of them - stability. Often there is an errors 1236, 1594. We fix one channel - another fails, sometimes it's critical.
Backups of most master databases are performed through ebs snapshot, where datadir located. But here another problem of mysql multi-source - work with backups, unlike multi instance replication, I can not just change datadir, where backup located.
I was trying to find a solution that at least partially solved the problems of stability and work with snapshots, but I found absolutely nothing.
Did I understand correctly that there is no support for multi-source replication in the aws-RDS?
Maybe there is a similar solution, or there is another approach to solving the problem (FEDERATED is bad variant). Thanks for any help and advices.
As Michael said, you shouldn't be encountering these errors. Multi source replication has quite stable now. I personally been using it for more than 2 years now. Yes I have faced some of issues like "slave trying to access binlogs that master has purged", but most of them were easy to sort out. I would recommend you to look at these replication topics:
Errant transactions
GTID hole : this was there because of bug
max allowed packet error
We fix one channel - another fails, sometimes it's critical.
make sure you're not touching GTID set for other channels.
Did I understand correctly that there is no support for multi-source
replication in the aws-RDS?
The feature still not available in any of AWS cloud services. https://forums.aws.amazon.com/thread.jspa?messageID=781416&tstart=0
Multi source replication is not supported in RDS , you can use AWS DMS for same purpose .
I've just setup MariaDB on Ubuntu VMs with Master-Master replication using a combination of these three guides:
http://www.chriscouture.com/setting-up-replication-on-mariadb/
https://www.server-world.info/en/note?os=Ubuntu_16.04&p=mariadb&f=3
https://www.digitalocean.com/community/tutorials/how-to-set-up-mysql-master-master-replication
In short, both are masters and both are slaves to the other one. This will be used by separate web hosting servers. One will be "primary master" which all web servers connect to, and in case of a failure on that server they will be manually changed to the "secondary master".
The reason I went for this instead of Master-Slave is
The 3rd party backup job is simpler. Both backups and restores are done on the "secondary" master, instead of backup from the secondary and restoring to the primary.
If the primary fails and I have to switch to the secondary for a while, all changes made during that time should be written to the primary when it comes online again (?).
It's not live yet but everything works fine so far when I'm testing it. However I'm no DBA. I've been reading about how it's not "worth it" and if you don't absolutely need the Master-Master you should go with Master-Slave.
Now I'm afraid I will run into problems like inconsistencies and other headaches.
A maximum of about 100 databases for mostly Wordpress installations will be hosted.
What are your thoughts on the matter? M-M or M-S?
If M-S, how do I "sync back" data changed if the Master goes down and the Slave need to be the active server for a period of time?
I'm also wondering if there's a standard, generally accepted, step-by-step way to upgrade these. I'm thinking when a OS or MariaDB version upgrade is needed.
My general thoughts are something like take down one server, upgrade it, start it. Then take down the other, upgrade it, start it.
But I'm guessing there's more to it than that.
I only found some documentation on M-S upgrading with Mysql.
I have question about data backup.
We are developing backed for mobile application.
So we have a few EC2 servers, one for api sub-domain and one for admin sub-domain. One RDS Mysql server for the database, also with 2 databases.
But I'm worried about one thing, RDS snapshots is good for database structure. If we will have some errors in application, or will need to revert some changes in structure.
I will just restore from yesterday snapshot. And how about content, because its adding every minute.
Maybe some one can describe mechanism or tools to prevent data our lost. Replications or something like that.
I think I've found the answer - bin log
https://dev.mysql.com/doc/refman/5.5/en/binary-log.html
I have a MySQL database running on our server at this location.
However, the internet connection at this location is slow (Especially when several users are connected remotely).
We also have a remote web server on a very fast internet connection.
Can I run another MySQL server on the remote server and still be able to run queries and updates on it?
I want to have two servers because
- Users at this location can connect via lan (fast)
- Users working remotely can connect to synced remote server (fast)
Is this possible? From what I understand replication does not work this way. What is replication used for then? Backups?
Thanks for your help!
[Edit]
After doing some more reading, I am a little worried about setting up multi-master replication due to the fact that I had not considered multi-master when designing the database and conflicts could be an issue.
The good news though is that most time consuming operations are queries not updates.
And, I found out that there is a driver that handles master-slave connections.
http://dev.mysql.com/doc/refman/5.1/en/connector-j-reference-replication-connection.html
That way writes will be sent to the master and reads can come from the faster connection.
Has anyone tried doing this before? My one concern is that if I update to the master, then run a query expecting to see the update on the slave, will it be there right away? Or will the slow connection make this solution just as slow as using the master for both read and write?
What you're asking, I believe, is called Multi-Master Replication, by which both servers serve as replication masters to each other. Changes on either server become replicated back to the other as soon as possible. MySQL can be configured to do it, however I'm not sure how the differences in speed would affect your performance and data integrity.
http://dev.mysql.com/doc/refman/5.1/en/mysql-cluster-replication-multi-master.html