Warner's questions

What options are there for session handling with a modern .NET IIS Web architecture?

I understand that IIS' native session support loses sessions upon restart. Furthermore, Microsoft recommends sessions be stored in the database, which is my preferred solution.

I am attempting to architect a highly available .NET IIS platform, which scales horizontally for a third party application. The application is developed externally and while I can push for storing in a database but that will not be possible for an immediate deadline.

The third party recommends using persistent sessions, which is something I avoid. Sticky sessions will lessen availability, as when the Web server becomes unavailable it will cause accessibility issues to the clients that were previously using it. Moreover, it lessens the load balancing functionality, as a single server may receive potentially more requests than the others. IIS will still lose sessions upon restart, which is something I would prefer to eliminate. I also do not want to store the session in a cookie on the client side.

I want to enable complete high availability, while still allowing application deployment to idle servers without impact. Additionally, full load balancing. Can I enable this functionality on this technology platform without rewriting the application? What options do I have?

When either selecting a data center as a co-location facility or designing a new one from scratch, what would your ideal specification be?

Fundamentally, diversified power sources, multiple ISPs, redundant generators, UPS, cooling, and physical security are all desireable.

What are the additional key requirements that someone might not consider on the first pass?

What are the functional details someone might not consider during the initial high level design?

I'd like to approach this from the perspective of designing a large data center or seeking a facility that was designed perfectly from an infrastructure perspective. This question has already been addressed with smaller facilities and workspace considerations here.

I have been researching high availability (HA) solutions for MySQL between data centers.

For servers located in the same physical environment, I have preferred dual master with heartbeat (floating VIP) using an active passive approach. The heartbeat is over both a serial connection as well as an ethernet connection.

Ultimately, my goal is to maintain this same level of availability but between data centers. I want to dynamically failover between both data centers without manual intervention and still maintain data integrity.

There would be BGP on top. Web clusters in both locations, which would have the potential to route to the databases between both sides. If the Internet connection went down on site 1, clients would route through site 2, to the Web cluster, and then to the database in site 1 if the link between both sites is still up.

With this scenario, due to the lack of physical link (serial) there is a more likely chance of split brain. If the WAN went down between both sites, the VIP would end up on both sites, where a variety of unpleasant scenarios could introduce desync.

Another potential issue I see is difficulty scaling this infrastructure to a third data center in the future.

The network layer is not a focus. The architecture is flexible at this stage. Again, my focus is a solution for maintaining data integrity as well as automatic failover with the MySQL databases. I would likely design the rest around this.

Can you recommend a proven solution for MySQL HA between two physically diverse sites?

Thank you for taking the time to read this. I look forward to reading your recommendations.