[Info-vax] How would you load balance excess webserver traffic between multiple OpenVMS servers?

[Arne Vajhøj]

On 1/11/2021 7:12 AM, D W wrote:
> There are MULTIPLE different approaches to doing this. Most involve
> HTTP (web) cookies and may involve DNS round robin load balancing or
> load balancers.
> 
> But how would this be accomplished using Apache or another web
> package on OpenVMS?
> 
> Would you use the same approach?

If HTTP requests for a given URL need to be spread out on multiple
web servers then some sort of load balancing is required.

In the IT industry in general having a dedicated load balancer or
having a network box in front with an embedded load balancer doing it
is common.

I am skeptical about DNS due to lack of handling of a web server
being down.

For VMS specifically there is also the cluster IP address, which
I have no idea whether will work well with a web server.

Cookies is not required for load balancing per se. If the requests
coming in are completely stateless then you don't need them. But if
there is state, then load balancers are usually able to route all
requests from same client to same web server (sticky session).

> Also if you house a DB like RDB on a separate OpenVMS server, what
> would be the fastest connect solution to obtain the fastest data
> transport rates between the DB server and other web servers?

There is no silver bullet.

On the web servers you need the application code & data to stay resident
in memory and reuse threads/processes to process requests as
starting processes and loading images are expensive. And
the database connections need to be managed by a connection pool
as open connection is expensive (note that a connection pool
also require application code& data resident in memory).

You need a fast network between web servers and database servers.
Preferably dedicated.

Having web servers on same servers as database is obviously the fastest
network as it is no network. But it also lock you into a N:N
relation ship between web and database servers instead of a more
flexible M:N. And it prevents you from putting in a firewall between
web and database servers, which your security people may really
like.

Arne