lambdas.yml is the file that points to lambda functions that you wrote.
Custom function goes under lambdas/ directory. If kes cannot find the file, it will throw an error like below:
Error zipping Error: ENOENT: no such file or directory, lstat 'lambdas/versionUpTest'
ENOENT: no such file or directory, lstat 'lambdas/versionUpTest'