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uni's avatar
uni
Icon for Altostratus rankAltostratus
Dec 03, 2013

Offline page as last resort with GTM

We have a requirement to present a service unavailable page when all GTM pool members are down, but can't really afford to dedicate new IP addresses at each site just for this.

 

There are two independent LTM sites, one GTM pool with the two LTM virtuals, using Global availability. My thoughts are to have each VS have an irule which responds with the site down page if no LTM-pool members are available.

 

Can someone suggest an efficient way to get the GTM to revisit the original pool members as a last resort, when the virtuals are marked red?

 

application delivery
BIG-IP DNS
design
gtm

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    • uni's avatar
      uni
      Icon for Altostratus rankAltostratus
      Dec 03, 2013
      Yes, but the complication is the GTM sees the virtuals as down, from iquery. Perhaps a better question is, can you get the GTM to use an LTM VS even if it is flagged down by iquery? The might also require you answering the question "Do I misunderstand how iquery works with LTM virtual status?"
  • IheartF5_45022's avatar
    IheartF5_45022
    Icon for Nacreous rankNacreous
    Dec 03, 2013

    Yes you can - using Fallback IP - you don't specify a virtual name, you specify an IP address. Even if that happens to be the same as a virtual that GTM thinks is down, it will return the Fallback IP as DNS response if your LTM virtuals are down.

     

    • uni's avatar
      uni
      Icon for Altostratus rankAltostratus
      Dec 03, 2013
      Yes, you're right. I had Last Resort Pool on my mind, so that's what I "read". So, what I thought was ideal, was to have a last resort pool, same members as the "main" pool, but then last resort members go 'red', and won't be used in the LB decision. We came up with a solution, but it is stretching the KISS principle a bit: gtm has a pool and last resort pool. Main pool monitors a url on the VS which is supplied by an irule depending on pool member availability. Last resort pool a simple http monitor. Virtuals have no default pool, they have a rule which responds to the gtm monitor request, and for other requests either responds with the offline page or sets the pool depending on member availability. I would love to hear a better way, and I will be impressed by anyone who tries to understand what I just wrote.
  • IheartF5_45022's avatar
    IheartF5_45022
    Icon for Nacreous rankNacreous
    Dec 03, 2013

    So why don't you use Fallback IP? The IP will be one of the virtuals from your main pool. On that LTM virtual will be an iRule that has an LB_FAILED event showing a sorry page. It will have a pool attached and so will show as up/down on LTM status.

     

    Seems way simpler than mucking about with Last Resort Pools on GTM and LTM virtuals with no default pool attached, and definitely fulfils the "can you get the GTM to use an LTM VS even if it is flagged down by iquery" issue unless there is more to it than that?

     

    • uni's avatar
      uni
      Icon for Altostratus rankAltostratus
      Dec 03, 2013
      But perhaps I should add, that doesn't cover all cases. Given fallback IP is that of vs-b, if vs-a goes down and ltm-b is down, we won't present the page, but potentially could if we can send traffic to ltm-a. This is such an unusual case though, and I decided it was not worth the mucking* around required. * Not actually the word I mean