Clustering with DRBD, Corosync and Pacemaker. Introduction. This article will cover the build of a two- node high- availability cluster using DRBD (RAID1 over TCP/IP), the Corosync cluster engine, and the Pacemaker resource manager on Cent. OS 6. 4. There are many applications for this type of cluster – as a free alternative to RHCS for example. However, this example does have a couple of caveats. As this is being built in a lab environment on KVM guests, there will be no STONITH (Shoot The Other Node In The Head) (a type of fencing). If this cluster goes split- brain, there may be manual recovery required to intervene, tell DRBD who is primary and who is secondary, and so on. In a Production environment, we’d use STONITH to connect to ILOMs (for example) and power off or reboot a misbehaving node.

I’m able to enable ssh, but I cant login. My hardware is a Iomega StorCenter ix2-200 2.1.25.229 and the “soho” prefix isn’t working. I was able to get the.

Quorum will also need to be disabled, as this stack doesn’t yet support the use of quorum disks – if you want that go with RHCS (and use cman with the two. The nodes used in this article are as follows: 1. Cent. OS 6. 4. 19.

Cent. OS 6. 4. 19. IP address. DRBD will be used to replicate a volume between the two nodes (in a Master/Slave fashion), and the hosts will eventually run the nginx webserver in a failover topology, with this example having documents being served from the replicated volume. Ideally, four network interfaces per host should be used (1 for “standard” node communications, 1 for DRBD replication, 2 for Corosync), but for a lab environment a single interface per node is fine. Let’s start the build . I presented a disk to each node (themselves running as KVM guests, as discussed earlier), at /dev/vdb – verified with fdisk - l.

We can now move on to software package installation. Package Installation. How To Install A Car Top Carrier Without Roof Rack. I installed pacemaker and corosync from the standard Cent.

OS repositories. # yum - y install corosync pacemaker. However, between Cent. OS 6. 3 and 6. 4 being released, pacemaker has been updated from 1. CRM shell is no longer included. This is now maintained in its own project – crmsh – and Cent.

• Introduction This article will cover the build of a two-node high-availability cluster using DRBD (RAID1 over TCP/IP), the Corosync cluster engine, and the Pacemaker.
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OS 6 RPMs are available via the Open. SUSE package repositories. So, I installed crmsh by way of its dependencies.

Cent. OS. A sample unicast configuration file is included at /etc/corosync/corosync. I took that file and edited as follows. On the first node: This command will sit waiting for entropy to be generated.

A quick way of doing this is to ssh in to the node via another session and run. Once the key is generated, it’ll be available at /etc/corosync/authkey. Copy it to the other cluster node, and secure it. Now, we can start our bare- bones cluster.

And verify the status. Last updated: Thu Jun 1. Last change: Thu Jun 1.

Stack: classic openais (with plugin). Current DC: rhcs- node. Version: 1. 1. 8- 7. Nodes configured, 2 expected votes. Resources configured. The cluster is running.

A quick check via the crm shell shows that there isn’t much to the configuration at this point. On both nodes, take a backup of /etc/drbd. I’ll just use /etc/drbd. As you can see, I have commented the configuration file directives very well, so will not explain them in this text apart from saying that the LVM logical volume at /dev/vg. You may also opt to use a separate volume for metadata for performance reasons. You can read the DRBD Internals page for more information on that.

For most simple applications, internal metadata will suffice. Start the DRBD service on both nodes (remembering that we will be shutting it down again as it will be cluster managed): On the MASTER NODE only, promote the volume to the primary role. Note that in DRBD versions < 8. You can cat /proc/drbdto watch the synchronisation operation in progress. GIT- hash: 7ad. 5f.

Build. 64. R6, 2. Connected ro: Primary/Secondary ds: Up. To. Date/Up. To. Date C r- -- -- . GIT- hash: 7ad. 5f.

Build. 64. R6,2. 01. Connected ro: Primary/Secondary ds: Up. To. Date/Up. To. Date. Cr- -- --    ns: 1. Or, run service drbd status. OK; device status. GIT- hash: 7ad. 5f.

Build. 64. R6, 2. Connected Primary/Secondary Up. To. Date/Up. To. Date C# service drbd statusdrbd driver loaded OK; device status: version: 8.

GIT- hash: 7ad. 5f. Build. 64. R6,2. 01. Connected  Primary/Secondary  Up. To. Date/Up. To. Date  COn both nodes, create the mountpoint for the DRBD- replicated volume, which in our case will be /data.

It is needless to say (but I’ll say it anyway) that this volume will be only ever mounted from a single node at a time. From the MASTER NODE, create an ext. Ensure that you use /dev/drbd. Next, the murky world of the cluster resource manager. Cluster Resource Configuration. Whilst there is lots of documentation available (both in articles like mine, and the excellent (and definitive) documentation at clusterlabs.

Clusters from Scratch), the CRM shell can still be a daunting place to be. Whilst there are GUI cluster resource configuration tools available, I much prefer to use the CRM shell due to the flexibility it offers. It is worth taking some time to learn the shell – you will be rewarded for doing so as you will have full control over your cluster. First off, as we’re only running a demo cluster and do not have any real fencing methods available to us, let’s disable STONITH. Let’s create our first resource – the failover IP address.

Using the ocf: heartbeat: IPaddr. There are parameters passed (an ip of 1. If you are ever unsure of which parameters and operations a resource agent supports, you can view extensive documentation via the crm ra meta < ra- name> command.

IPaddr. 21# crm ra meta ocf: heartbeat: IPaddr. Once the failover. What does this mean? Essentially – you, the sysadmin, know what you are doing, and have manually forced a move of a cluster- managed resource. The cluster manager therefore deems the current node unfit for purpose and creates a location constraint with a score of - INFINITY (negative- infinity) – the resource will never run there again. You can remove the constraint via the crm shell, or just fail it back with crm unmove resource < resource> which will also deem the node fit for purpose once again, and remove the constraint. Next, nginx. nginx Installation and Configuration.

At this point, I’ll install nginx as it’ll be the next clustered resource to be configured. RPMS/nginx- release- centos- 6- 0. RPMS/nginx- release- centos- 6- 0. Again, ensure that it doesn’t start automatically on boot, as the cluster will manage the nginx service: Reading the output of crm ra meta nginx, we learn that the agent works by polling /nginx. This is not present in the configuration provided by the nginx RPMs just installed, so we will need to add it manually. I configured it as per the Http. Stub. Status. Module documentation, with appropriate ACLs.

Quite a bit happened above. First, I configured another primitive (i. I specified a path to the configfile and the nginx binary (httpd=) and then specified various operations to define monitor, start and stop timeouts. Next, I created a colocation called nginx.

Colocations tell the cluster that resources need to be colocated on the same node. An affinity of INFINITY is specified – i. However, if we try to configure the multi- part DRBD resources like this, some of the configuration will be applied before the entire resource has been configured, which will not give us the desired result.

Therefore, I’ll take a copy of the current CIB configuration and make changes there on a “shadow instance”, verify, then commit back into the main cluster configuration. This is a much safer way of working, and should be used when making any significant change on a Production cluster. Let’s start by creating the shadow configuration instance.

INFO: drbd shadow CIB created. INFO: drbd shadow CIB createdcrm(drbd)#You can see that the crm prompt has changed from crm(live) to crm(drbd)indicating that we are working with the shadow instance. Next, I’ll create the DRBD primitive and a new type of resource – ms. Then, the monitor intervals for both master and slave are defined.