Clustering examples given bellow will work with any environment, physical or virtual. If you want to skip the cloud provider configuration, just search for BEGIN keyword and you will be taken to the cluster and OS specifics. As all High Availability Clusters, this one also needs some way to guarantee consistence among different cluster resources. Clusters usually do that by having fencing mechanisms: A way to guarantee the other nodes are not accessing the resources before services running on them, and managed by the cluster, are taken over. If following this mini tutorial for a Microsoft Azure Environment setup, make sure to have in mind that this example needs Microsoft Azure Shared Disk feature:. And then create then create the clubionicshared01 disk using provided yaml file example.
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Clustering examples given bellow will work with any environment, physical or virtual. If you want to skip the cloud provider configuration, just search for BEGIN keyword and you will be taken to the cluster and OS specifics.
As all High Availability Clusters, this one also needs some way to guarantee consistence among different cluster resources. Clusters usually do that by having fencing mechanisms: A way to guarantee the other nodes are not accessing the resources before services running on them, and managed by the cluster, are taken over. If following this mini tutorial for a Microsoft Azure Environment setup, make sure to have in mind that this example needs Microsoft Azure Shared Disk feature:.
And then create then create the clubionicshared01 disk using provided yaml file example. After those are created, next step is to create the 3 needed virtual machines with the proper resources, like showed above, so we can move on in with the cluster configuration. Important - this is just an example to show a bit of cloud-init capabilities. Feel free to change this at your will. Now it is time to configure the cluster network. In the beginning of this recipe you saw there were 2 subnet created in the virtual network assigned to this environment:.
Since there might be a limit of 2 extra virtual network adapters attached to your VMs, we are doing the minimum required amount of networks for the HA cluster to operate in good conditions. This means that every cluster node will have 1 IP from this subnet assigned to itself and possibly a floating IP, depending on where the service is running the resource is active.
This network is important as corosync relies on it to know if the cluster nodes are online or not. It is also possible to create a 2nd virtual adapter to each of the nodes for a 2nd ring in the cluster messaging layer. Depending on how you configure 2nd ring it may either reduce delays in message delivering OR duplicating all cluster messages to maximize availability.
Important - And that all interfaces are have to be configured as static despite being provided by the cloud environment through DHCP.
The lease renew attempts of a DHCP client might interfere in the cluster communication and cause false positives for resource failures. This means that all the network interfaces are being configured and managed by systemd. Unfortunately, because of bug LP: , currently being worked on, any HA environment that needs to have virtual aliases configured should rely in the previous ifupdown network management method.
This happens because systemd-networkd AND netplan. Instructions on how to remove netplan. Make sure you have something similar to:. Before restarting corosync service with this new configuration, we have to create a corosync key file and share among all the cluster nodes:.
Attention - Some administrators prefer NOT to have cluster services started automatically. Finally, it is time to check if the messaging layer of our new cluster is good.
With the messaging layer in place, itt is time for the resource-manager to be installed and configured. As you can see we have to wait until the resource manager uses the messaging transport layer and defines all nodes status. Give it a few seconds to settle and you will have:.
For Ubuntu Bionic this is the preferred way of configuring pacemaker. At anytime you can execute crm and navigate a pseudo filesystem of interfaces, each of them containing multiple commands. Important - Explaining what the watchdog mechanism is or how fencing works is beyond the scope of this document.
Do have in mind that an high availability cluster has to be configured correctly in order to be supported AND having the correct amount of votes in a cluster split scenario AND a way to fence the remaining nodes is imperative. Nevertheless - For this example it is mandatory that pacemaker knows how to decide which side of the cluster is the one that should be still enabled WHEN there is a problem in one of the participating nodes.
In our example we will use 3 nodes so each remaining 2 nodes can form a new cluster when fencing 1 possible fenced node. After configuring watchdog, lets keep it disabled and stopped until we are satisfied with our cluster configuration. This will prevent our cluster nodes to be fenced by accident during resources configuration. By telling pacemaker we have a watchdog device , and what is our fencing policy , we also have to configure a fence resource that will be running at the cluster.
Make sure all the applications that will be managed by pacemaker agents do have their data in the shared disk to be used. Make sure the shared disk has the same name in all cluster nodes. That is not a good practice as the disks might get another device name in other boots. Having 3 keys registered show that all the 3 nodes have registered their keys while, when checking which host holds the reservation, you have to see a single node key:.
It is very important we are able to fence nodes. In our case, as we are also using a watchdog device, we want to make sure that our fenced node will reboot in access to the share scsi disk is lost.
With that information, network communication of that particular node can be stopped in order to test fencing and watchdog suicide. Before moving on, check:. Okay 1 worked. Now we are going to install a simple web server lighttpd service in all the nodes and have it managed by pacemaker. The idea is simple : to have a virtual IP migrating in between the nodes, serving a web server lighttpd service with files coming from the shared filesystem disk.
Having the hostname inside index. And we will have a good way to tell from which source the lighttpd daemon is getting its files from:. Next step is to configure the cluster as a HA Active-Passive only cluster. The shared disk in this scenario would only work as:. As you can see I have created 2 resources and 1 group of resources. You can copy and paste the command from above crmsh example and do a commit at the end, it will create the resources for you.
Important - Note that, in this example, we are not using the shared disk for much: only to have a fencing mechanism.
This is important, specially in virtual environments that does not give you a power fencing agent, OR this power fencing agent could introduce unneeded delays in all operations: then you should rely in SCSI fencing and watchdog monitoring to guarantee cluster consistence.
The agents list will be compatible with the software you have installed at the moment you execute that command in a node as the systemd standard basically uses existing service units from systemd on the nodes.
And, in this particular case, it should be tested in the node that you did all the LVM2 commands and created the EXT4 filesystem:. Now we can create the resource responsible for taking care of the LVM volume group migration: ocf:heartbeat:LVM-activate. In my case it got enabled in the 2nd node of the cluster:.
Its time to configure the filesystem mount and umount now. Before moving on, make sure to have installed psmisc package in all nodes. And this is what makes our new cluster environment perfect to host any HA application: a shared disk that will migrate in between nodes allowing maximum availability: as the physical and logical volumes migrate from one not to another, configured services also migrate.
It is time to go further and make all the nodes to access the same filesystem in simultaneously from the shared disk being managed by the cluster. This allows different applications - perhaps in different resource groups - to be enabled in different nodes simultaneously while accessing the same disk.
It may cause problems by rebooting your cluster nodes. In order to install the cluster filesystem GFS2 we will be able to remove the configuration we did in the cluster again!
This package provides the clustering interface for LVM2 , when used with corosync based eg Pacemaker cluster infrastructure. Important - I created the resource groups one by one and specified they could run in just one node each.
Another possibility would be to have those 2 services started by systemd on each node but then the service restart would have to be done by systemd in case of software of these daemons problems. This allows multiple hosts to share a VG on shared devices.
The lockspace segment maximum 30 characters is a unique file system name used to distinguish this gfs2 file system. We can now go back to the previous - and original - idea of having lighttpd resources serving files from the same shared filesystem. Having multiple instances on the same node would imply in having different configuration files and different.
Instead of having 3 lighttpd instances here, you could have 1 lighttpd, 1 postfix and 1 mysql instance and all instances floating among all cluster nodes with no particular preference.
You now have a pretty cool cluster to play with! Author: Rafael David Tinoco rafaeldtinoco ubuntu. In the beginning of this recipe you saw there were 2 subnet created in the virtual network assigned to this environment: clubionicnet Virtual network subnets: - private Ubuntu Networking ifupdown VS netplan.
Press keys on your keyboard to generate entropy. Make sure no reservations are in place for the shared disk you will use Make sure all the applications that will be managed by pacemaker agents do have their data in the shared disk to be used Make sure the shared disk has the same name in all cluster nodes.
This cluster behavior is usually to avoid the "ping-pong" effect for intermittent failures. Configure Resources in Pacemaker Now we are going to install a simple web server lighttpd service in all the nodes and have it managed by pacemaker. About to write GPT data. Do you want to proceed? The operation has completed successfully. Configuring the filesystem resource agent Perfect.
Are you sure you want to proceed? Ubuntu HA - Introduction.
Ubuntu High Availability
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