See the website.
This talk was given by Moshe Zadka from VMware.
Think about how to crash and then recover from the crash.
If your application recovers quickly, stuff can crash and no one will see.
Even Python code occasionally crashes due to C bugs, untrapped exceptions, infinite loops, blocking calls, thread deadlocks, inconsistent resident state, etc. These things happen!
Recovery is important.
A system failure can usually be considered to be the result of two program errors. The second error is in the recovery routine.
When a program crashes, it leaves data that was written in an arbitrary program state.
Avoid storage: caches are better than master copies.
Databases are good at transactions and at recovering from crashes.
File rename is an atomic operation in modern OSs.
Think of efficient caches and reliable masters. Mark cache inconsistency.
He seems to be skeptical of the ACID nature of MySQL and PostgreSQL. I'm not sure why.
Don't write proper shutdown code. Always crash so that your crash code always gets tested. Your data should always be consistent.
Availability: if the data is consistent, just restart.
To get into the high 9s, recover very quickly. Limit impact, detect the crash quickly, and startup quickly.
Vertical splitting: different execution paths, different processes. Apache can have a child process die with no impact on availability.
Horizontal splitting: different code bases, different processes.
Watchdog: monitor -> flag -> remediate.
Watchdog principle: keep it simple, keep it safe.
A process can touch a file every 30 seconds. The watchdog sees whether the file has been touched.
The watchdog and the processor restarter should not be in the same process, because the watchdog should be simple. Remember: separation of concerns.
Mark problems. Check solutions. See if restarting worked.
Everything crashes: plan for it.
Linux has a watchdog daemon. Use that to watch your watchdog.