I have more than one application server for smooth access but unfortunate at time i faced problem of duplication in tickets: my current scenario generates ticket no. after the completion of form at save events but sometime due to server issues , replication delays hence two ticket generated of same no.
Normally this question is way to broad as it does not show the minimum amount of research...
Nevertheless I will answer it: Here are some ways to solve this issue.
The easiest: Add a Servername to the ticket-number.
So count as you do, but if there are duplicates, then they are different by there servername part:
Server1-0001 Server1-0002 Server2-0003 Server3-0004 Server1-0005 Server2-0005
Another possibility is to create the number only on ONE server. You can either do this by having an agent on that server running on all documents that do not have a number yet or "asking" the server for a number when saving.
First is easy to implement, but on the servers that do not create the numbers it will take at most 2 replication intervals for a ticket to get its unique number.
Second is trickier as you need all servers to "know" one central server and write code / agents / whatever to "get" a ticket number from that server and put it in the ticket.
All of this is not trivial and therefor to broad to answer in detail here.