How can I execute some code at the end of each epoch?

Question

I'd like to make some RPC calls a few slots after the end of each epoch. This is mainly to do with staking rewards calculations.

How can I get a callback into my code on each new epoch (once every two or three days)?

None of the things I can subscribe to on the WS API look quite right. I can subscribe to slots, but I don't want 432,000 callbacks just to check on which one the epoch number incremented. Can I find a program that executes near the start or end of each epoch (and preferably not that much the rest of the time) and use programSubscribe to listen for that?

Answer 1

There is no generic functionality for callbacks on Solana, so you must create something external which listens to the chain in some way.

External products such as Cronos http://cronos.so/ exist to solve this exact problem.

If you want an easy solution, you can just write a simple program that polls the block height every few minutes, and does extra work if the height matches some critera (ie. within the first 100 hundred slots of the epoch).