SSHFS on command line usually takes the ssh key with the -o, option which doesn’t really work when adding it in fstab. If you look around the internet you most probably found that people recommend adding fstab records with the -o option, but this wont work, simply add the key as another regular fstab option –

sshfs#USER@domain.com:/data/www /mnt/logs/  fuse IdentityFile=/home/USER/.ssh/id_rsa,uid=UID,gid=GUID,users,idmap=user,noatime,allow_other,_netdev,reconnect,ro 0 0 

Replace USER with the user who connects to the remote server and UID and GUID with the ones from the remote server.
The above also mounts the remote system as read-only so you wont be able to write on the mount.