Friday, October 17, 2008

Configuring A Basic HACMP Cluster On AIX Unix

Hey there,

Today we're going to go back to the AIX well (which we haven't visited since our fairly-old post on working with AIX LVM. That post links back to a bunch of other posts in the series, but it "has" been about 3 months since we've touched on the AIX OS, which is grossly disproportionate to the amount of attention Solaris, Linux and Open Source Software get. Perhaps, someday, I'll work on it enough that I'll feel more comfortable digging into its guts. ...figuratively, of course ;)

This little how-to post isn't meant to cover all the angles of cluster setup and configuration that there are to cover. If it were, that would be (aside from slightly-more-than-presumptuous) a long long long post. Your children would have children while you tried to remain interested ;) This is a simple little "get started" guide and only meant for a simple 2 node cluster. If you want to get fancier, visit IBM's HACMP Knowledge Base where they've got more documentation than you could ever wish for. Check the bottom of the post for some other good resource sites.

First things first (before we get to step one), as with any other sort of cluster setup (VCS, SunCluster, etc) you'll need to determine what you want from your cluster. That's beyond the scope of this post (or the other ones we just referenced), but you should have a clear plan of attack. Know what you want and everything you can think of that it might take to get there (in this case 2 nodes for redundancy and uptime - On the flipside, what we're looking to do here, which is also very important, is to just set up the basics of our cluster and disk heartbeats. The network is up and running, cabled and doing well. This is one "huge" assumption, but it just means less for us to have to soak up in one sitting :) It's always a good idea to write a list. ...unless you're in the habit of losing your lists, in which case you should keep everything in your head where you'll retain most everything until you lose "it." (And you can take that either way ;)

NOTE: We're going to be running through this using an AIX CLI utility called "smit." Of course, it's more of a TUI (Terminal Based User Interface) than real CLI, but, while you're using it, you can make it show you the underlying commands it's running with judicious use of the F6 key. Copy and paste all that stuff into a script and amaze your friends :)

1. Choose one node from which to do your configuration. It can be either of the two we're going to use (host1 or host2). It's important that you stick with your choice, though.

2. Check for any possible HACMP configuration already on the host (just in case) by using smit (called as smitty):

NOTE: For this how-to, we'll represent menu choices (drill-down) using tabs for each level down, and set them in boldface type. Oh, yes, and step two will fail if there are no cluster components to remove. It'll make you feel all warm and cozy inside, though ;)

host1 # smitty hacmp
Extended Configuration
Extended Topology Configuration
Configure an HACMP Cluster
Remove an HACMP Cluster

3. Then, proceed to configure the topology of your cluster (For us, this simply means two nodes sharing a heartbeat address)

host1 # smitty hacmp
Extended Configuration
Extended Topology Configuration

4. Here you have a few different things to do (under Extended Topology Configuration):
Configure an HACMP Cluster
<-- You'll need at least two hosts to create a cluster and you can't have more than one cluster per pair of hosts (Only 1 for 2).
Configure HACMP Nodes
<-- Be sure to use your boot IP address in the "communication path" field. We haven't gotten to the virtual IP yet

5. Now, on each node of your cluster (host1 and host2), be sure to start the clcomdES service if it isn't running already (might be on host1 since we're configuring the cluster on it, but shouldn't be on host2)

To check for it, type:

host1 # lssrc -s clcomdES

To start it , type:

host1 # startsrc -s clcomdES

6. Now go back up one level (to Extended Configuration) and run through these options (You can just ignore the ones we don't mention):

Configure HACMP Network
<-- Add your public, or virtual Ethernet network information here. Be sure to configure the subnet mask appropriately and set "Enable IP Address Takeover via IP Aliases" equal to "yes." Also, unset (leave or make blank) the "IP Address Offset for Heartbeating over IP Aliases" setting.

Configure HACMP Interfaces and Devices
<-- if you find any old, or strange, node names in here, delete them. They're probably from a previous setup. You can keep them, but they might cause you headache later on. Note that you'll generally only see this type of behaviour if the machine has been cloned. You can also manually define interfaces here (if you choose), but you should have already done that under "Configure HACMP Network" above. If you need to add any interfaces here, just choose "Add Pre-defined interface" and go to town :)

Configure HACMP Persistent Node IP Label/Address
<-- This should be the address associated with your host's DNS name (not the cluster's DNS name!).

7. Now add service addresses for all of the service types you want to host on your cluster (Services are generally disk, network, etc - resources you want to share within your cluster and keep highly available) Add Service addresses for each of the services you want to host - we're only dealing with disk and IP here.

host1 # smitty hacmp
Extended Configuration
Extended Resource
Configuration HACMP Extended Resources Configuration
Configure HACMP Service IP Labels/Addresses

Here, add a volume group solely dedicated to providing disk-based heartbeat! Name it whatever you want, like "host1-diskhb" and make sure it's type is set to "Enhanced-Capable Concurrent Volume Group." You won't ever actually need this volume group for anything (disk storage, etc, I mean), but making it this type of volume prevents it from being discovered. You "Do Not" want to share your host's disk heartbeat device!

8. Now, proceed to configure your disk heartbeat network (this part practically does the work for you. Just keep stabbing at those keys ;)

host1 # smitty hacmp
Extended Configuration
Extended Topology Configuration
Configure HACMP Networks
Add a Network

9. Next, add devices to our disk heartbeat network:

host1 # smitty hacmp
Extended Configuration
Extended Topology Configuration
Configure HACMP Communication Interfaces/Devices
Add Communication Interfaces/Devices
Add Pre-defined Communication Interfaces and Devices
Communication Devices

Choose the (hopefully, at this point) only heartbeat network available :) Name the device whatever you want (again, we'll go with host1-diskhb), supply the logical path to the device (if necessary) and supply the name of one of your nodes when required to. Note that this will trigger an error the first time you run it (This is perfectly normal!). It will state the obvious in a slightly different manner, but your error message will basically say that you can't have only one device defined, since two are required). The simple fix: Run step 9 again exactly, except pick your other node's name when required to. Now you have two members in your disk heartbeat network.

10. Now, set up your basic networking:

host1 # smitty hacmp
Further Configuration
Static routes
Add a Static Route

Make sure to set your "Destination Type" to "net," your "Destination Address" to "default" and set the "Default Gateway" to the IP address of your default router (Same as when you set up your persistent host address in step 4 - Note that it's not shown in the documentation here, but will be there if you follow the smitty-steps down to the correct menu level :)

11. And you're set. Just for caution's sake, you should do some simple testing by running:

host1 # smitty hacmp
Extended Configuration
Extended Verify and Synchronization

Accept the defaults here and your changes and setup will be verified and synchronized with every node in your cluster (In our case today, the "other one" ;)

And you're good to go :)

Remember, our little experiment here was a very quick and dirty how-to with very limited scope. If you want an equally expedient, but more comprehensive and wide-ranging, look at setting up HACMP fast, check out TriParadigm's HACMP Configuration Page. It's a lot better than this one, but may be too much if you're just getting started (?) :)



Please note that this blog accepts comments via email only. See our Mission And Policy Statement for further details.