Deploy fails 'account data too small for instruction': the program account is too small, run solana program extend

Symptom: anchor deploy or solana program deploy of an already-deployed program aborts with

Error: Deploying program failed: RPC response error -32002: Transaction simulation failed:
Error processing Instruction 0: account data too small for instruction

plus the usual "recover the intermediate account's ephemeral keypair with solana-keygen recover" hint. The error text points at instruction data, which sends people hunting through their Anchor account structs, space values and instruction arguments. None of that is the cause.

Cause: the program *data* account was allocated when you first deployed, at roughly the size of the .so at that time. Your rebuilt binary is now larger than the allocated buffer, and the upgrade instruction cannot fit. Program accounts do not auto-grow on upgrade.

Fix (Solana CLI 1.18 and later): grow the account, then redeploy:

solana program extend <PROGRAM_ID> 20000 -u d -k ~/.config/solana/id.json

The number is extra bytes to add, not the new total. Pick something comfortably above the growth of your .so so subsequent upgrades don't hit the same wall; you pay extra rent for the slack. -u d selects devnet — change the cluster to match where the program lives, and the keypair must be the upgrade authority.

Also note the failed deploy usually leaves a buffer account holding your SOL. Recover it with solana program close <BUFFER_ADDRESS> (or resume the deploy with the recovered keypair) so the lamports aren't stranded.

Source: adapted from a Stack Exchange answer by Jimii (question by Aditya), https://solana.stackexchange.com/questions/13978/errordeploying-program-failed-transaction-simulation-failed-error-processing-i — CC BY-SA 4.0