For a given vip is it possible to define pool of servers that are active and also some pool of members that passive. Basically this is what I want to do: 1. Define active pool of servers for a vip 2. Define passive pool of servers for a vip 3. When all the members in pool go down then make passive pool active Is it possible to do that in LTM? If it's possible then when one of the pool members (previously active) become active again does it switch it back?

Hi Manc, Yes it's definitely doable with LTM. You can do this either 2 ways : iRule or point-n-click configuration. Point-n-click method Basically you setup a single pool that is configured for Priority Load balancing For Example: You have 4 servers and you want 2 of the servers active all the time, but as soon as 2 of them fail due to the health check, then the other 2 servers come on line. If the 2 primary servers come back then return the traffic. The structure would be Pool A Server 1 Priority 100 ratio 1 Server 2 Priority 100 ratio 1 Server 3 Priority 50 ratio 1 Server 4 Priority 50 ratio 1 You would probably add persistence so that you don't abruptly move connections during a failback and rather wait for the existing connection to close. However, this all depends entirely on the application requirements for persistence. There are more details on how to do this on the F5 Configuration Guide you can find on http://ask.f5.com iRule Method The reason why you would want to use iRules is that is basically allows you even more granular control over how you want configure your active/passive configuration. Here is a simple example when CLIENT_ACCEPTED { if { [active_members active_pool ] >= 1 } { pool active_pool } else { pool passive_pool } } This iRule assumes you have defined 2 different pools. I hope this helps Bhattman

There is another available option that is close to what you are requestion using the Priority Activation Groups. It will keep a specified number of servers available and on-line (basically keeping your load distributed rather than continually loading it onto the last server and slowing down performance until it either fails, is taken off-line, or the other active servers become available again). Available option on the Pool settings. Under Load Balancing the "Priority Group Activation" to "Less than..." and then select the number of members you always want active. Then go to each node and change the Priority Group for each server. Example: If I set the Priority Activation Group to Less than 3 the Load Balancer will always keep 3 servers available. (Higher the Activation Group the higher the preference) 10.10.10.1 - Priority Activation Group 3 10.10.10.2 - Priority Activation Group 3 10.10.10.3 - Priority Activation Group 3 10.10.10.4 - Priority Activation Group 2 10.10.10.5 - Priority Activation Group 2 10.10.10.6 - Priority Activation Group 2 10.10.10.7 - Priority Activation Group 1 10.10.10.8 - Priority Activation Group 1 10.10.10.9 - Priority Activation Group 1 If one server in Group 3 dies, then a server from Group 2 will be begin to take traffic. If two servers in Group 3 die, then two servers in Group 2 will be begin to take traffic. and so on.... This is basically an Active / Standby ability.

Thanks! Is it possible to configure it such that Group 2 server takes over only when all the servers in Group 3 are down?

I believe so... This is the description giving for Priority Activation Groups: Specifies, when enabled, that the system load balances traffic across activated members of their priority group. To enable priority group activation, select Less than from the list, and type the number of members below which the system activates the group. Once you enable priority group activation, you can use options on the Member Properties screen to assign each member to a priority group. The system sends traffic to members in priority-group order. I believe that if you select Less than 0, that it will not activate anything in the next group until there are 0 available members of the previous group. NOTE: As soon as a member of a Higher Priority Group recovers, traffic will begin flowing back to the Higher Priority Group. (This should happen with new connections. It will not shift the current traffic currently connected to servers in a Lower Priority Group). I would suggest testing it to verify (I've never drained one group to zero before transferring the load to a new group. I use it more as an Hot Standby Activation), but it should do what you are wanting. You can see the current load on each member of a pool by going to the following: v9.x Overview -> Statistics Statistics Type: Pools v10.1.x Overview -> Statistics -> Local Traffic Statistics Type: Pools

Can LTM be used to configure Active and Passive Servers?

rudysetiawan_79
Nimbostratus
May 10, 2010
As for me, we have a primary farm and secondary farm.

When the primary farm is unavailable, I want LTM to be able to start directing to the backup farm.

Since the website is using 1 IP, can both farms share the same vip and still maintaining the failover mechanism?

And also to add "primary farm is unavailable" means that when LTM found a blank page when it tried to query the members.

Thank you
Michael_Yates
Nimbostratus
May 10, 2010
Manc,

I don't think that you can do what your planning with a Single Virtual Server or a Single Pool.

LTM -> WS 1 - 4 -> DB1

LTM -> WS 5 - 10 -> DB2

You would need 2 Virtual Servers and 2 Pools in order to do this (but then you would have to figure out how to balance the load between these Virtual Servers):

LTM -> Virtual Server 1 (10.10.10.10) - Pool 1 (WS 1 - 4) -> DB1

LTM -> Virtual Server 2 (20.20.20.20) - Pool 2 (WS 5 - 10) -> DB2

If you wanted to do something similar with a single Virtual Server and a Single Pool you could configure the following:

Priority Activation Group - Less than.... 5

10.10.10.1 - Priority Activation Group 2

10.10.10.2 - Priority Activation Group 2

10.10.10.3 - Priority Activation Group 2

10.10.10.4 - Priority Activation Group 2

10.10.10.5 - Priority Activation Group 2

10.10.10.6 - Priority Activation Group 1

10.10.10.7 - Priority Activation Group 1

10.10.10.8 - Priority Activation Group 1

10.10.10.9 - Priority Activation Group 1

10.10.10.10 - Priority Activation Group 1

This would keep five servers active and five servers on Hot-Standby (which is somewhat of an overkill). A failure would be less disruptive (and more evenly distrubute the load) if all of the servers were active in the pool at the same time.

Rudysetiawan,

Yes. Primary and Secondary Farm's can share the same Virtual Server in the scenario that you are describing. See Bhattman's iRule earlier in this discussion chain for one method and an iRule Example.

I am unsure what you mean by this:

And also to add "primary farm is unavailable" means that when LTM found a blank page when it tried to query the members.

Did you want something put into the LTM Log? If so, you can add to Bhattman's iRule example. This will put a comment into the F5 LTM Log located in /var/log/ltm

when CLIENT_ACCEPTED { if { [active_members active_pool ] >= 1 } { pool active_pool } else { log local0. "Primary Farm is Unavailable" pool passive_pool } }
manc_63343
Nimbostratus
May 17, 2010
We also use GTM. Do you think we can do something like that GTM instead of LTM? Is that much simpler? We could have ratio or have it set to global availability with multiple members listed in the pool
Michael_Yates
Nimbostratus
May 18, 2010
Unfortunetly I can't help you with that.

My company purchased the GTM Module, but they haven't let us use it :-(

Perhaps one of the others could answer that for you.
JCMATTOS_41723
Nimbostratus
Aug 27, 2010
Bhatman,

I had a similar situation, where I wanted to manually disable and/or force offline the active servers (not relying on the monitor failing). But still achieve a failover to the passive pool members. Is this possible? If not, how can I enable this? Also, is it true that upon re-enabling the active servers the active connections will immediately and abruptly failback to the active pool members? If so, how can I gracefully allow the connections on the passive pool members finish? Appreciate your help. Thx!
shawn306_84070
Nimbostratus
Apr 04, 2011
I wanted to bump this up and ask a question.

I have a pool with two servers in it. One would be active and one would be used only if the other server goes down.

The one server has the priority group set to 1

The other server has a priority group setting of 0

For Priority Group Activation does the number need to be set at 2 or 3 or does it make a difference ?

Also can I force offline the non-active server and have it re-activate automatically if the main server goes down ?

Thanks

Shawn
shawn306_84070
Nimbostratus
Apr 04, 2011
I wanted to bump this up and ask a question.

I have a pool with two servers in it. One would be active and one would be used only if the other server goes down.

The one server has the priority group set to 1

The other server has a priority group setting of 0

For Priority Group Activation does the number need to be set at 2 or 3 or does it make a difference ?

Also can I force offline the non-active server and have it re-activate automatically if the main server goes down ?

Thanks

Shawn
Austin_Geraci_3
Cirrus
Apr 04, 2011
I'm not sure what would happen if you set it to 0.. I always started at 1, and the doc I have speaks to starting at one..

I would set the primary server as 2, and secondary as 1... Yeah you could use 2 or 3 for primary.. just as long as the numbers are higher for the primary.. more numbers are for more tiers.. Then set your less than attribute to 1.

One thing to note, when a group comes available all members in with that priority come online.. for example.. let's say less than criteria is met and group 1 comes online and it has 3 members all three members come online.... conversely, if you're primary(higher) group has 3 members with an attribute of less than 3, and one server goes offline, the next group would come online, and the reaming members in the primary group would stay online as well..

Also can I force offline the non-active server and have it re-activate automatically if the main server goes down ?

without using an iRule I don't believe there is a way to employ a server when you manually disable it.. anyone know different?
Michael_Yates
Nimbostratus
Apr 04, 2011
Question: For Priority Group Activation does the number need to be set at 2 or 3 or does it make a difference?

Answer: The higher the number the higher the preference. I have some that start at 1 and go upwards. I also have a few that start a 0 (I follow the practice outlined by iRuleYou. I start at one as a common practice for consistency, some of my co-workers don't....hence the ones that start with 0).

Question: Also can I force offline the non-active server and have it re-activate automatically if the main server goes down?

Answer: There have been many posts for this. You can attempt to disable a server with an iRule, but the health check applied in the pool will put it back on-line shortly after you disable it (if I am wrong somebody set me straight because I would love to be wrong on this one). The only way to fully put down a server is to take it out of the pool, stop the service that is being monitored on the server, or apply a health monitor that will fail (forcing the server to appear as hard down).

I have never attempted to apply or remove a Health Monitor with an iRule. I am not sure if it could be done.
hooleylist
Cirrostratus
Apr 05, 2011
Posted By JRahm on 04/04/2011 08:36 AM

I haven't tested dest addr persistence, but seems it would do the job as well.

http://devcentral.f5.com/wiki/default.aspx/iRules/SingleNodePersistence.html Click Here

I think destination address persistence is done based on the client's destination address (before translation is performed to the pool member IP. So I think it's only useful if the VS isn't doing translation.

Aaron