librarian-puppet install with destructive mode doesn't make atomic changes

[lelutin]

Currently, librarian-puppet install when used with the destructive mode does not use an atomic action when replacing the install_path. As seen in the install action0, it starts by removing everything and creating a new empty directory and then recreates all of the modules.

This means that during the whole time that librarian-puppet is recreating all of the module directories, lots of things are missing! If one is using librarian-puppet on the puppetmaster, this can impact puppet clients that start their run during this period: some modules are missing entirely, causing errors, and in some more dire cases some things can end up being modified on the client because of the missing bits.

I think librarian-puppet can do a bit better. one method would be to create a temporary directory right beside the install_path, place all of the files in that temp dir, and then once everything is done and no errors happened, rename the current install_path to take it out of the way, and rename the temp dir as the new install_path. This renaming operation would make the change atomic. once the rename is done, the install action could remove the tmp dir.

[anarcat]

A workaround is to deploy librarian stuff to another directory and then swap the directories, something like this:

https://redmine.koumbit.net/projects/git-hooks/repository/revisions/master/entry/post-receive-puppet-r10k#L57

The magic code is:

sudo "${SCRIPT_DIR}"/swap_puppet_branches "$TMPDIR" "$DEPLOYDIR" "$GRAVEYARD_DIR" 

Which basically swaps the temporary deployment directory with the temp directory, moving the old deployment directory to a "graveyard".

Earlier, there's also a hack to use a shared cache for librarian:

                git clone --branch="$branch" "${ORIG_GIT_DIR}" "$TMPDIR"
                if [ ! -z "${LIBRARIAN_TMP_DIR}" ] ; then
                    mkdir -p "${LIBRARIAN_TMP_DIR}"
                    ln -s "${LIBRARIAN_TMP_DIR}" '.tmp'
                    umask 002 '.tmp'
                fi

It would be useful to have a setting to tell librarian where to find its cache to avoid such a hack.