[Info-vax] Distributed and Clustered App Design (was: Re: WHY IS VSI REQUIRING A HYPERVISOR FOR X86 OPENVMS?)

Stephen Hoffman seaohveh at hoffmanlabs.invalid
Mon Jan 4 15:42:32 EST 2021


On 2021-01-04 18:17:29 +0000, Simon Clubley said:

> So it's the same as always in that you also need the additional 
> supporting infrastructure to provide what you get as standard with VMS 
> clustering, including being able to detect when a node has only 
> temporarily failed (in order to prevent everything that comes with that 
> situation) when that temporarily failed node comes back online.

I did a presentation on this topic way back 'round Y2K at a DECUS symposium.

It's rather more involved than the lock manager—electing a primary is a 
piece of this, certainly.

LAN failover via IP and formerly DECnet, DNS and formerly DECdns, 
application-level routers, host-based RAID-1 (HBVS), and various other 
pieces can and usually are involved.

OpenVMS isn't all that good at 802.3ad link aggregation, either. But I digress.

Not much has changed with OpenVMS and clustering, which is both good and bad.

Bad: having done this more than a few times, OpenVMS DLM is a pain in 
the arse to use, and I know how to use it for this and related 
requirements.

There's still too little doc here. What doc is available is scattered 
across a half-dozen manuals.

Things have changed on other platforms in the ensuing decades, though.

Apache ZooKeeper (variously with Curator) is in use, Paxos sometimes 
gets mentioned around this, Linux has a cluster DLM, and approaches 
such as Mosquitto try to avoid even having a primary. Sometimes LDAP 
and Kerberos for authentication, too.

For those with an interest in this topic area:
https://www.coursera.org/lecture/cloud-computing-2/1-3-election-in-chubby-and-zookeeper-IDKhR 

https://openreplica.org
https://en.wikipedia.org/wiki/Apache_ZooKeeper
https://en.wikipedia.org/wiki/Apache_Spark
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/high_availability_add-on_overview/ch-dlm 

etc.

TL;DR: OpenVMS DLM is still nice albeit in need of better abstractions, 
but DLM is no longer a particularly distinguishing feature.


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Pure Personal Opinion | HoffmanLabs LLC 




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