Load Balancing Strategy FIFO

[vuduy]

Hello,

Is it possible to setup HAProxy to use load balancing strategy FIFO? What that means is supposed that I have 3 backend servers: A, B, and C.

• It will load balance to A first
• If A is down, then will load balance to B and when A comes back up, it will be added to the end of the line.
• If B is down, then it will load balance to C and when B comes back up, it will be added to the end of the line
• At any time, all successful connections will only go to the same server

Thanks.

[lukastribus]

Use the backup keyword allong with -on-marked-* :

http://cbonte.github.io/haproxy-dconv/2.4/configuration.html#5.2-backup
http://cbonte.github.io/haproxy-dconv/2.4/configuration.html#5.2-on-marked-down
http://cbonte.github.io/haproxy-dconv/2.4/configuration.html#5.2-on-marked-up

However, when the primary server comes back up, servers will go back to that one.

[vuduy]

That is not useful then. If A comes backup, existing connections will stay in B and new connections will go to A. Whenever a server goes back online, it must go to the end of the queue hence FIFO.

At any time, all successful connection will only go to the same server

[lukastribus]

@vuduy

That is not useful then. If A comes backup, existing connections will stay in B and new connections will go to A

That’s why we have, like previously mentioned:

on-marked-down shutdown-sessions on-marked-up shutdown-backup-sessions

@vuduy

Whenever a server goes back online, it must go to the end of the queue hence FIFO.

This is currently not an option.

@vuduy

At any time, all successful connection will only go to the same server

This is possible and very common, with the configuration mentioned above.

[vuduy]

I think you are mistaken. If A goes down, some clients will connect to B; once A comes back up, new clients will connect to A and existing connections still stay connected to B.

How does that meet my requirements that at any times, successful connections only goto the same server? When some are connected to B and some connected to A (when it came back up).

[vuduy]

Just want a clarification; if you use on-marked-up shutdown-backup-sessions, how long is the delay? Will there be any time when both servers (A and B) can have connected clients?

Also, if you designate B and C as backup; and if A goes down, then B gets all the connections; if B also goes down, will C gets all the connection? And if B comes back up? Will both B & C get connections? Only when A comes back online, then connections on B & C get terminated and re-connected to A?

[lukastribus]

@vuduy

I think you are mistaken. If A goes down, some clients will connect to B; once A comes back up, new clients will connect to A and existing connections still stay connected to B.

No, on-marked-up shutdown-backup-sessions will kill existing connections to B.

@vuduy

if you use on-marked-up shutdown-backup-sessions , how long is the delay?

There is no delay.

@vuduy

Will there be any time when both servers (A and B) can have connected clients?

No.

@vuduy

if A goes down, then B gets all the connections; if B also goes down, will C gets all the connection?

Yes.

@vuduy

And if B comes back up? Will both B & C get connections?

B will get the connections, and connections on C would be terminated.

@vuduy

Only when A comes back online, then connections on B & C get terminated and re-connected to A?

Yes.

The use-case of the shutdown-backup-sessions and shutdown-sessions features is to have all connections on one server. If there is a situation where this is not the case, then it’s a bug.