This post is part of a series exploring the unique aspects and capabilities of WebSphere Liberty when running on z/OS.
We'll also explore considerations when moving from WebSphere traditional on z/OS to Liberty on z/OS.
The next post in the series is here.
To start at the beginning, follow this link to the first post.
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Suppose that one fine day when your servers are all just purring happily along that something goes awry. You know what it is. You know how to fix it. But work is flooding in and making the problem worse. If you could just stop getting new requests into a particular server for just a couple of minutes you could fix it and then let it go again. What to do?
Well, you could just shut down the server. But chances are automation will see the server stop and just restart it. That’s probably all going to happen way too fast. Plus it looks like an unplanned outage to somebody that cares about that sort of thing. Wouldn’t it be nice to just tell the server ‘hold on a minute here’?
Well, you can. You can do this with the ‘server’ script but on z/OS it is easier from the operator console to issue a Modify command directed at the server you care about and tell it to ‘pause’. Without parameters it will just stop all the HTTP and MDB listeners. The server stays up, but it just stops taking new work for a while. When you’re ready, you can use the matching ‘resume’ Modify command to start the listeners up again. The server stays up the whole time.
The HTTP ports are going to close which might raise some issues and you might want to think about where those connection requests are going to go and how that might look upstream from you. For MDB listeners the work will just pile up on the queue while the listeners are paused.
If you forget what you did, you can issue a related ‘status’ Modify command to find out the pause/resume state of things.
What if that’s just too much though? What if you’ve got both HTTP and MDB work coming into the server and it is just one of them you want to stop? Or perhaps you have several HTTP listeners defined and only want to stop one (or two, whatever) of them?
Well, you can do that too. The configuration element of the HTTP and MDB listeners all have an ‘id’ attribute and the Modify pause/resume commands allow you to specify those ids as a string of ‘target’ values. This allows you to selectively pause/resume listeners within the server. Here that ‘status’ command might be more useful to make sure you got the ones you wanted or that you resumed all the ones you paused.
And that’s all there is to it.