[pgpool-general: 2045] Re: Suggestion about two datacenters connected through WAN

[Mistina Michal]

Hi Tatsuo.

>> Hi.
>> 
>> I was considering using pgpool in our environment, but I don't know if 
>> it is the best idea. I would appreciate some suggestions, pros, cons 
>> of the solution using pgpool. Or is there another way how to do it?
>> 
>>  
>> 
>> We have 2 technical centers TC1 and TC2. In each runs postgres server.
>> Technical centers are connected with WAN link. 
>> 
>> Clients are connecting through postgres JDBC driver to the TC1. If TC1 
>> goes down JDBC driver will connect to TC2 automatically. Each 
>> technical center has the IP address from other subnet.
>> 
>> We need to have replicated data from postgres in TC1 to postgres in TC2.
>> 
>> Moreover:
>> 
>> -          TC1 can act as read-write server
>> 
>> -          TC2 can act as read server
>> 
>> -          after TC1 goes down TC2 should became read-write -> this
>> FAIL-OVER should be automatic
>> 
>> -          FAIL-BACK procedure doesn't have to be automatic. we can do it
>> manually
>> 
>>  
>> 
>> I know the fine way with manual fail-over can be postgres streaming 
>> replication from TC1 to TC2. However I expect the pgpool can add more 
>> control over automatic fail-over and better control for manual fail-back.
>> 
>>  
>> 
>> My questions.
>> 
>> Is the aforementioned scenario possible to build using pgpool?

>Yes. You set up pgpool server on TC1 and TC2.

>> Can pgpool fail-over to the IP address from different subnet? I mean 
>> not providing virtual IP address but making TC2 as R/W.

>Yes.

Is it possible to set up TC1 in read-write and TC2 in read mode by using
pgpool replication mode or is it possible only by using master/slave mode?
I ran into some issues by using postgresql streaming replication so I would
like to avoid it if it is possible.

>- If pgpool/TC2 detects TC1 goes down, it will automatically promote
>  PostgreSQL/TC2 by properly setting "failover script" on TC2.

>- After TC1 goes up again, you can use "online recovery" feature of
>  pgpool to sync PostgreSQL/TC1 with PostgreSQL/TC2. After resync,
>  PostgreSQL/TC1 will become the standby server(read only).

>> If it is possible I will have more questions while building it :)

>Sure:-)


Best regards,
Michal Mistina


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