Lock your swarm to protect its encryption keyEstimated reading time: 5 minutes
In Docker 1.13 and higher, the Raft logs used by swarm managers are encrypted on disk by default. This at-rest encryption protects your service’s configuration and data from attackers who gain access to the encrypted Raft logs. One of the reasons this feature was introduced was in support of the new Docker secrets feature.
When Docker restarts, both the TLS key used to encrypt communication among swarm nodes, and the key used to encrypt and decrypt Raft logs on disk, are loaded into each manager node’s memory. Docker 1.13 introduces the ability to protect the mutual TLS encryption key and the key used to encrypt and decrypt Raft logs at rest, by allowing you to take ownership of these keys and to require manual unlocking of your managers. This feature is called autolock.
When Docker restarts, you must unlock the swarm first, using a key encryption key generated by Docker when the swarm was locked. You can rotate this key encryption key at any time.
Note: You don’t need to unlock the swarm when a new node joins the swarm, because the key is propagated to it over mutual TLS.
Initialize a swarm with autolocking enabled
When you initialize a new swarm, you can use the
--autolock flag to
enable autolocking of swarm manager nodes when Docker restarts.
$ docker swarm init --autolock Swarm initialized: current node (k1q27tfyx9rncpixhk69sa61v) is now a manager. To add a worker to this swarm, run the following command: docker swarm join \ --token SWMTKN-1-0j52ln6hxjpxk2wgk917abcnxywj3xed0y8vi1e5m9t3uttrtu-7bnxvvlz2mrcpfonjuztmtts9 \ 172.31.46.109:2377 To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions. To unlock a swarm manager after it restarts, run the `docker swarm unlock` command and provide the following key: SWMKEY-1-WuYH/IX284+lRcXuoVf38viIDK3HJEKY13MIHX+tTt8
Store the key in a safe place, such as in a password manager.
When Docker restarts, you need to unlock the swarm. You will see an error like the following and services will not start.
$ sudo service docker restart $ docker service ls Error response from daemon: Swarm is encrypted and needs to be unlocked before it can be used. Please use "docker swarm unlock" to unlock it.
Enable or disable autolock on an existing swarm
To enable autolock on an existing swarm, set the
autolock flag to
$ docker swarm update --autolock=true Swarm updated. To unlock a swarm manager after it restarts, run the `docker swarm unlock` command and provide the following key: SWMKEY-1-+MrE8NgAyKj5r3NcR4FiQMdgu+7W72urH0EZeSmP/0Y Please remember to store this key in a password manager, since without it you will not be able to restart the manager.
To disable autolock, set
false. The mutual TLS key and the
encryption key used to read and write Raft logs will be stored unencrypted on
disk. There is a trade-off between the risk of storing the encryption key
unencrypted at rest and the convenience of being able to restart a swarm without
needing to unlock each manager.
$ docker swarm update --autolock=false
Keep the unlock key around for a short time after disabling autolocking, in case a manager goes down while it is still configured to lock using the old key.
Unlock a swarm
To unlock a locked swarm, use
docker swarm unlock.
$ docker swarm unlock Please enter unlock key:
Enter the encryption key that was generated and shown in the command output when you locked the swarm or rotated the key, and the swarm unlocks.
View the current unlock key for a running swarm
Consider a situation where your swarm is running as expected, then a manager node becomes unavailable. You troubleshoot the problem and bring the physical node back online, but you need to unlock the manager by providing the unlock key in order to read the encrypted credentials and Raft logs.
If the key has not been rotated since the node left the swarm, and you have a
quorum of functional manager nodes in the swarm, you can view the current unlock
docker swarm unlock-key without any arguments.
$ docker swarm unlock-key To unlock a swarm manager after it restarts, run the `docker swarm unlock` command and provide the following key: SWMKEY-1-8jDgbUNlJtUe5P/lcr9IXGVxqZpZUXPzd+qzcGp4ZYA Please remember to store this key in a password manager, since without it you will not be able to restart the manager.
If the key was rotated after the swarm node became unavailable and you do not have a record of the previous key, you may need to force the manager to leave the swarm and join it back to the swarm as a new manager.
Rotate the unlock key
You should rotate the locked swarm’s unlock key on a regular schedule.
$ docker swarm unlock-key --rotate Successfully rotated manager unlock key. To unlock a swarm manager after it restarts, run the `docker swarm unlock` command and provide the following key: SWMKEY-1-8jDgbUNlJtUe5P/lcr9IXGVxqZpZUXPzd+qzcGp4ZYA Please remember to store this key in a password manager, since without it you will not be able to restart the manager.
swarm, manager, lock, unlock, autolock, encryption
Warning: When you rotate the unlock key, keep a record of the old key around for a few minutes, so that if a manager goes down before it gets the new key, it may still be locked with the old one.