12 Nov
2019
12 Nov
'19
2:52 p.m.
Right now the way ceph-daemon is used by the ssh orchestrator is designed
to minimize the dependencies/setup complexity. The only requirements for
a host to be added to the cluster are
- python (2 or 3)
- systemd
- either podman or docker installed
- the ceph cluster's pub key in /root/.ssh/authorized_keys
No other software (including Ceph) needs to be installed. The mgr/ssh
module invokes ceph-daemon on the remote host by running /usr/bin/python
over ssh and piping the cluster's version of ceph-daemon to stdin.
The downside to this approach is that some users might not like the idea
of ceph having an ssh key with root access. For large clusters I'm not
sure how much this really matters--if you pwn ceph you can delete TB to PB
of data so do you really care if someone has root?--but for hyperconverged
cases this might be a problem.
One alternative might be to
- create a ceph user on the node, and put the cluster's key in
that user's authorized_keys
- install a package that includes ceph-daemon (/usr/bin/ceph-damaen)
- install an /etc/sudoers.d/ceph file that lets the ceph user
'sudo ceph-daemon ...'
Cons:
- This makes the bootstrap process slightly more complicated: (1) install
package, (2) create user, (3) install ssh key (vs just #3).
- The remote version of ceph-daemon can get out of sync with the
cluster.. either stale and missing some feature, or even too new and
not behaving the way the cluster expects.
Pros:
- This limits the attack surface area (if someone manages to get the
cluster's ssh key) to the functions that ceph-daemon implements, vs
full root.
We could mitigate the 'keep ceph-daemon up to date' problem somewhat by
implementing a 'ceph-daemon update' function that will apt/dnf/yum install
ceph-daemon on the local host, so that the cluster could self-update the
remote host.
Or... we could skip the package entirely and install the ceph-daemon
script in /home/ceph/ceph-daemon, and include an update function that
updates the script in place. That is less complicated than knowing how to
apt/dnf/yum install a package for all the random distros and repo location
combinations (one of the biggest benefits of containers IMO). But it
still requires some sort of process to keep ceph-daemon up to date.
Maybe if we always pass an md5sum to ceph-daemon whenever we invoke it to
assert that we are running the version we want, and if there is a
mismatch, ceph-daemon bails out with a special exit code that triggers and
update and retry?
Anyway, what are people's thoughts here? How much more complicated are we
interested or willing to make this to make people more comfortable with
the idea that ceph owns an ssh key?
sage