lsyncd + s3

lsyncd.conf.lua

s3sync = {
    maxProcesses = 1,
    onStartup = "aws s3 sync ^source ^target",
    onCreate  = "[ -f ^source^pathname ] && aws s3 cp ^source^pathname ^target^pathname || true",
    onModify  = "[ -f ^source^pathname ] && aws s3 cp ^source^pathname ^target^pathname || true",
    onDelete  = "[ -f ^source^pathname ] && aws s3 rm ^target^pathname || true",
    onMove    = "aws s3 mv ^target^o.pathname ^target^d.pathname",
}

sync {
    s3sync,
    source = "/path/to/source",
    target = "s3://your-bucket-name/path/to/target",
}

Oh actually, from my reading of the docs, || true might not be needed at all? (except for onStartup, if that's what you want):

By default Lsyncd ignores all exit codes except onStartup which must return 0 for it to continue.

fyi, there has been a documentation update with example: lsyncd/lsyncd#463