GTM upgrade from v.11 to v.12 (2 site not consecutively)

Hi

 

We have 4 GTM v.11 reside in 2 different site. (HA-pair each site)

 

May I ask how to upgrade these GTM to v.12?

 

Please correct my step. 1. renew device certificate and copy to each box (if it expired) <---- Is this need to be done?

 

1. disable synchronisation and DNS zone synchronisation on each box.

    

2. Upgrade HA pair in first site normally.

    

3. After finish on first site. run big3d_install on box v.12 on first site to make it install new big3d version on box v.11 on second site. <---- can v.11 run new big3d version?

    

4. Testing v.12 on first site.

    

5. Upgrade HA pair in second site normally. <----- the thing is I can't upgrade two site consecutively. I've to wait around 4-6 hour after upgrade on first site. Is this will cause a problem?

    

6. After finish on second site. enable synchronisation and DNS zone synchronisation on each box.

    

7. testing v.12 on second site.

    

Thank you very much Ker