The question “what problems will I have when migrating to the cloud” gets asked often enough. If by cloud you mean Amazon EC2, then from a technical perspective there isn’t much that changes. The biggest thing that changes is just how you pay your bill.
Having said that, there’s still a few potential gotchas:
- There are no Virtual IP addresses. Most High Availability tools (like MMM or DRBD+Heartbeat)
work on the principal of having a floating IP address which is used for the application to connect to the current master. With EC2, you can’t do this.
- There’s no customization of the memory. The maximum amount of memory you can have is 15GB, so some users with larger working sets may find this a limitation. If you look at the Dell online store, it costs $2094 to upgrade an R900 from 4G memory to 64G (or $4378 to upgrade to 128G) which justifies that some problems are best solved by just throwing memory at them. With EC2, you can’t do this.
- Even the largest instance types have slow disks. Related to the point above – you can’t change the disks either. Both software RAID striping the internal disks on an extra large EC2 instance or using striped EBS volumes is still going to be slower than a good RAID 10 controller with a battery backed write cache.
If you can live with these three things, then hopefully your migration should work smoothly. If you can’t free yourself from these limitations, then perhaps you should either look at a cloud hosting provider that can host non-virtualized servers for you in the same data center, or hold tight for the moment.
