High availability on remote site

[Matthew Seaman]

On 15/08/2013 12:19, Olivier Nicole wrote:
> I have been assigned to offer HA on a 3 tiers architecture.
> 
> Data storage tier will be MySQL, so replication is easy.
> 
> HA should be implemented only on the Data storage tier, Active/Active,
> but one of the sites is remote!
> 
> When everything is working, each application accesses the local MySQL
> tier, but when the local MySQL becomes unavailable, it should be able
> to automatically move to the other database server.
> 
> I have no access to the application, so I cannot modify it to test if
> local MySQL is working. So I should have an HA mechanism that enforces
> changing the IP address on the database server.
> 
> If both servers are installed at different places, with different
> addresses, would there be a way beside establishing an IP tunnel/VPN
> between both places to have all machines in a single subnet?
> 
> An image is here http://www.cs.ait.ac.th/~on/HA.gif
> 
> I am really bothered by the IP tunnel, but that's the only way I see to keep HA.
> 
> Any idea welcome.

Depending on the technology use in you middle layer, it may be quite
simple.  Some application languages, eg Java allow you to specify a
list of servers in a DB connection string.  The server names will be
tried in order until a successful connection is made.

Other languages may provide a similar facility, or it should be pretty
easy to code up with minimal intervention in your codebase required.

	Cheers,

	Matthew