Developing with cephadm

There are several ways to develop with cephadm. Which you use depends on what you’re trying to accomplish.

vstart –cephadm

  • Start a cluster with vstart, with cephadm configured

  • Manage any additional daemons with cephadm

In this case, the mon and manager at a minimum are running in the usual vstart way, not managed by cephadm. But cephadm is enabled and the local host is added, so you can deploy additional daemons or add additional hosts.

This works well for developing cephadm itself, because any mgr/cephadm or cephadm/cephadm code changes can be applied by kicking ceph-mgr with ceph mgr fail x. (When the mgr (re)starts, it loads the cephadm/cephadm script into memory.)

MON=1 MGR=1 OSD=0 MDS=0 ../src/ -d -n -x --cephadm
  • ~/.ssh/id_dsa[.pub] is used as the cluster key. It is assumed that this key is authorized to ssh with no passphrase to root@`hostname`.

  • cephadm does not try to manage any daemons started by (any nonzero number in the environment variables). No service spec is defined for mon or mgr.

  • You’ll see health warnings from cephadm about stray daemons–that’s because the vstart-launched daemons aren’t controlled by cephadm.

  • The default image is, but you can change this by passing -o container_image=... or ceph config set global container_image ....

cstart and cpatch

The script will launch a cluster using cephadm and put the conf and keyring in your build dir, so that the bin/ceph ... CLI works (just like with vstart). The script will tear it down.

  • A unique but stable fsid is stored in fsid (in the build dir).

  • The mon port is random, just like with vstart.

  • The container image is$tag where $tag is the first 8 chars of the fsid.

  • If the container image doesn’t exist yet when you run cstart for the first time, it is built with cpatch.

There are a few advantages here:

  • The cluster is a “normal” cephadm cluster that looks and behaves just like a user’s cluster would. In contract, vstart and teuthology clusters tend to be special in subtle (and not-so-subtle) ways.

To start a test cluster:

sudo ../src/

The last line of this will be a line you can cut+paste to update the container image. For instance:

sudo ../src/script/cpach -t

By default, cpatch will patch everything it can think of from the local build dir into the container image. If you are working on a specific part of the system, though, can you get away with smaller changes so that cpatch runs faster. For instance:

sudo ../src/script/cpach -t --py

will update the mgr modules (minus the dashboard). Or:

sudo ../src/script/cpach -t --core

will do most binaries and libraries. Pass -h to cpatch for all options.

Once the container is updated, you can refresh/restart daemons by bouncing them with:

sudo systemctl restart ceph-`cat fsid`.target

When you’re done, you can tear down the cluster with:

sudo ../src/   # or,
sudo ../src/cephadm/cephadm rm-cluster --force --fsid `cat fsid`

Note regarding network calls from CLI handlers

Executing any cephadm CLI commands like ceph orch ls will block the mon command handler thread within the MGR, thus preventing any concurrent CLI calls. Note that pressing ^C will not resolve this situation, as only the client will be aborted, but not execution of the command within the orchestrator manager module itself. This means, cephadm will be completely unresponsive until the execution of the CLI handler is fully completed. Note that even ceph orch ps will not respond while another handler is executing.

This means we should do very few synchronous calls to remote hosts. As a guideline, cephadm should do at most O(1) network calls in CLI handlers. Everything else should be done asynchronously in other threads, like serve().