howto/fabric.md

@@ -410,3 +410,62 @@ Time and labor.
 ### Perl
 
  * notoriously hard to read
+
+### mitogen
+
+A late-comer to the "alternatives considered" section, I actually
+found out about the [mitogen](https://mitogen.networkgenomics.com/) project after the choice of Fabric
+was made, and a significant amount of code written for it (about 2000
+[SLOC](https://en.wikipedia.org/wiki/Source_lines_of_code)).
+
+A major problem with Fabric, I discovered, is that it *only* allows
+executing **commands** on remote servers. That is, it's a glorified
+shell script. Yes, it allows things like SFTP file transfers, but
+that's about it: it's [not possible to directly execute Python code on
+the remote node](https://github.com/fabric/fabric/issues/237). This limitation makes it hard to implement more
+complex business logic on the remote server. It also makes error
+control in Fabric less intuitive as normal Python code reflexes (like
+exception handling) cannot be used. Exception handling, in Fabric, is
+particularly tricky, see for example [issue 2061](https://github.com/fabric/fabric/issues/2061) but generally:
+exceptions don't work well inside Fabric.
+
+Basically, I wish I had found out about mitogen before I wrote all
+this code. It would make code like the LDAP connector much easier to
+write (as it could run directly on the LDAP server, bypassing the
+firewall issues). A rewrite of the post-install grml-deboostrap hooks
+would also be easier to implement than right now.
+
+Considering there isn't that much code written, it's still possible to
+switch to Mitogen. The major downside of mitogen is that it doesn't
+have a commandline interface: it's "only" a Python library and
+everything needs to be written on top of that. In fact, it seems like
+Mitogen is primarily written as an Ansible backend, so it is possible
+that non-Ansible use cases might be less supported.
+
+The "makefile" (`fabfile`, really) approach is also not supported at
+all by mitogen. So all the nice "self-documentation" and "automatic
+usage" goodness brought to use by the Fabric decorator would need to
+be rebuilt by hand. There are existing dispatchers (say like
+[click](https://click.palletsprojects.com/en/7.x/) or [fire](https://github.com/google/python-fire)) which could be used to work around that. 
+
+And obviously, the dispatcher (say: run this command on all those
+hosts) is not directly useable from the commandline, out of the
+box. But it seems like a minor annoyance considering we're generally
+rewriting that on top of Fabric right now because of [serious](https://github.com/fabric/fabric/issues/2071)
+[limitations](https://github.com/fabric/fabric/issues/2069)  in the current scheduler.
+
+Finally, mitogen seems to be better maintained than fabric: at the
+time of writing:
+
+| Stat         | Mitogen    | Fabric     |
+|--------------|------------|------------|
+| Last commit  | 2020-07-30 | 2020-01-20 |
+| Last release | 2019-11-02 | 2019-08-06 |
+| Open issues  | 119        | 385        |
+| Open PRs     | 12         | 47         |
+| Contributors | 18         | 10         |
+
+The Fabric author also posted a [request for help](http://bitprophet.org/blog/2020/07/02/help-wanted/) with his
+projects, which doesn't bid well for the project in the long term. A
+few people offered help, but so far no major change has happened in
+the issue queue (lots of duplicates and trivial PRs remain open).