You want to execute SSH commands from the build environment to a remote server You want to rsync files from the build environment to a remote server If anything of the above rings a bell, then you most likely need an SSH key.

Available documentation suggests that ED25519 is more secure.

There is a serious weakness in DSA (which extends to ECDSA) that has been exploited in several real world systems (including Android Bitcoin wallets and the PS3); the signature algorithm relies on quality randomness (bits that are indistinguishable from random); once the PRNG enters a predictable state, signatures may leak private keys. Systems that use ECDSA must be aware of this issue, and pay particular attention to their PRNG.