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As a python dev who deploys a lot of software, I found this article to be wonderfully helpful and informative, and a good reflection of current best practices.
Summary of the deployment tools mentioned:
- Manage remote daemons with supervisord
http://supervisord.org/
- Manage python packages with pip (and use `pip freeze`)
http://pypi.python.org/pypi/pip
http://www.pip-installer.org/en/latest/requirements.html
- Manage production environments with virtualenv
http://www.virtualenv.org/
- Manage Configuration with puppet and/or chef
http://puppetlabs.com/
http://www.opscode.com/chef/
- Automate local and remote sys admin tasks with Fabric
http://fabfile.org
- Don't restrict yourself to old Python versions to appease your tools / libs.
- Strongly consider rolling your own DEB/RPMs for your Python application.
- Celery for task management
http://celeryproject.org/
- Twisted for event-based python.
http://twistedmatrix.com/trac/
- nginx / gunicorn for your python web server stack
http://www.nginx.com/
http://gunicorn.org/Chef requires Ruby programming. Puppet doesn't, but the core is obviously Ruby, and you extend it using Ruby.
You may possibly like my new project:
The core is Python but you can write modules in any language.
There is also cuisine, which brings chef-like functionality to fabric.
Yes to all of this and I'll throw in my two cents on our web server setup which is nginx + uwsgi (which has served remarkably well).
I use gevent instead of twisted for event-based python. Gevent is a lot nicer to work with and doesn't make your code less readable in the way twisted does with its callbacks and errbacks. It's also a lot easier to do unit testing with gevent.
I don't get the negativity on using your distro's packages, at least from the staying-stable perspective. Any decent package manager should let you pin/hold critical packages on a particular version, so if "the next Ubuntu ships with a different SQLAlchemy by default" you just hold the SQLAlchemy package at the version you want and then ignore it until you're ready to make that move.
99% percent of the time when I hear people complaining about their distro's packages, the complaints are coming from the opposite direction -- they want to run something bleeding-edge and the distro doesn't have it yet. (This is the standard beef Rubyists have with Debian, for instance -- that code that just hit Github ten minutes ago isn't in Debian's repos yet.)
It's usually best to leave these packages for the system python to run pieces of the system. There's one exception that I usually make for this rule: packages with complex C dependencies. NumPy is the first package that comes to mind. I usually prefer to just use the package manager to deal with that.
The worst thing about them is the fact that they are installed into global site-packages that you shouldn’t use for any serious coding.
And yes, they are mostly outdated too.
Oh the problem has NOTHING to do with "10 minutes ago".
Ubuntus's latest release 11.10 (yes I know 12.04 is a couple of days away) is Python 2.4. I don't remember what Ruby it is, but it's something like ~=1.8.7. Ruby is on 1.9.3 and the next version of Rails won't even support 1.8.7.
I'd be fine with a year or two old Python and Ruby....
They rarely have a modern enough package to be worthwhile. When you control the package pipeline, you have the ability to dictate how modern or conservative your software is.
The problem is that most programming languages (especially Python and Ruby) are ecosystems unto themselves and often move at a much faster pace than any stable distro (or LTS) could keep up with. That's why we have gems and pip.
Cf. Ubuntu LTS MongoDB default is like 1.2 or something. This is why I switched to using 10gen's repo.
Regarding virtualenv, I have come to the conclusion that Linux containers are robust enough now (like freebsd jails say two or three years ago) that I don't need to virtualise just python - I can afford to have the whole server as a "virtualenv" - no need for that extra complexity just install into site packages. No conflicts because a whole instance is dedicated. Jails take this to the limit - one virtual machine, one process - say Bind. A vulnerability in Bind ? The attacker takes over ... Nothing.
Sorry, but I'm not sure I understand your logic. Using virtualenv adds extra complexity, but virtualizing the entire server doesn't? I mean, the only complexity using virtualenv adds is having to run the virtualenv process once. After that, you can still install to site-packages. You just have to install to a different site-packages directory.
Besides that, it's worth pointing out that using a virtualenv is not a security precaution. It's a precaution to prevent mucking up the global python installation for other packages that run on it. Using linux containers to achieve this seems like overkill.
Regarding "Don't use ancient system Python versions" and "Use virtual environments", you can knock out two birds with one stone by just using pythonbrew. It also saves you the hassle of rolling your own deb/rpm if a package doesn't happen to exist.
Also, Chef/Puppet aren't "alternatives" to something like Fabric. Use the former for server provisioning, and use the latter for actually kicking off the deployment process. Trying to shoe-horn the finer deployment steps (git checkout, tarballing, symlinks, building the virtualenv, etc) into Chef was a nightmare every time I tried. Those tasks are better suited for Fabric's imperative design. Plus you can just run any Chef commands from Fabric itself, or use something like pychef for finer grained control. It's a win/win.
Fabric seems to be the most popular deployment tool, yet the author advises against it without giving any reason why.
I'd love to see some proper detail in the article around why.
And not in the vein of "Chef/Puppet are better", but more along the line of "here's what can go wrong with Fabric".
> Those tasks are better suited for Fabric's imperative design.
Yes they are, but IMHO not on the target servers.
I use Fabric to build DEBs that get deployed by Puppet. I prefer to have no build tools on target servers, YMMV.
> [...] you can knock out two birds with one stone by just using pythonbrew
> The trick is to build a debian package (but it can be done using RPMs just as well) with the application and the whole virtualenv inside.
I would love to read an article describing some best practices for doing that. I tried it once and found it extremely difficult, reverting to a git checkout + virtualenv kind of deployment.
Check out git's "make rpm" target.
https://github.com/gitster/git/blob/master/Makefile
Hosting your own apt/yum repo is pretty simple.
Does anyone have an example of a similar "make deb" target they could share?
I've heard of git-dpm and git-buildpackage but haven't used them extensively myself. They're the debian git packaging tools.
It will come, I promise.
Long-time Python user here.
For a lot of my projects I write a shell script which builds all of the application dependencies (including services) into a project directory and run them all from there.
It takes a little bit of work to get going --- especially when building a new service for the first time --- but I like that it side-steps language-specific packaging tools (particularly the half-baked Python ones) and lets me pin an applications dependencies and port to various environments (develop on Mac, deploy on Unix) almost exactly. Integrating with Puppet/Chef is just a matter of breaking up the shell script into pieces.
We do this, but also add a couple layers of safety between us and PyPI:
1. Run your own secure, local pypi clone with exact source versions of the packages you use.
2. The packages for production are built into RPMs from the local pypi.
PyPI is great for discovery, getting things running quickly, and testing new versions, but you never want to rely on it, even for development.
I'd really enjoy reading about how to setup a PyPI mirror like the one you use in your development/deployment workflow. It seems like a really good idea, considering I've had problems with PyPI at really inconvenient times in the past.
Yeah, plus it speeds package building up and protects against not-so-occasional pypi outages.
I don't think using virtualenv to jam everything into a big deb file is really a best practice.
But at the end of the day, I do have to do a lot of that with application deployment, but I try to only go as far as packaging libraries (ie. gems, jars, python equiv) in the rpm/deb file.
RHEL 6 is python 2.6.6, btw.
What happens when there are vulns for your stack?
> What happens when there are vulns for your stack?
That’s a good point and the answer is: You have to monitor your dependencies of public services (that aren’t that many).
But you have to do that anyway, because I can’t explain to our customers that their data has been hacked because Ubuntu/Red Hat didn’t update Django (fast enough).
My two cents: I am a developer + ops person and deploy Python apps all the time. Typically they are Django and Tornado services. On top we also have a lot of daemons and a ton of library code.
I agree with the OP on most points but do not on a few. First DO use packages that come with the OS. The OP says that you should not have the distro maintainers dictating what you use. I say, use what is widely available. It takes the headache out of a lot of your deployments. If you are looking for a library that converts foo to bar look in your distro's repos before going on GitHub. Your sysadmin will thank you.
Second, DO NOT use virtualenv. It fixes the symptoms (Python's packaging system has many shortcomings such as inability to uninstall recursively, poor dependency management, lack of pre and post install scripts, etc.), but not the problem. Instead, use distro-appropriate packages. Integrate your app into the system. This way you will never end up running a daemon inside a screen session, etc. You also get the ability to very nicely manage dependencies and a clean separation between code and configuration.
Lastly, DO use apache + mod_wsgi. It is fast, stable, widely supported and well tested. If apache feels like a ball of mud, take the time to understand how to cut it down to a minimum and configure it properly.
When it comes to infrastructure, making boring choices leads to predictable performance and less headaches more often than not (at least in my experience).
"First DO use packages that come with the OS."
I'd go middle ground, and start here, but consider a self-built package where necessary. It depends in part on the focus of your distro.
virtualenv. What problem does it solve? Different python version/environments? Wouldn't that be better solved with another (virtual) server? I understand if an extra $20/month is an issue, but otherwise ...
> First DO use packages that come with the OS. The OP says that you should not have the distro maintainers dictating what you use. I say, use what is widely available. It takes the headache out of a lot of your deployments. If you are looking for a library that converts foo to bar look in your distro's repos before going on GitHub. Your sysadmin will thank you.
The sysadmin will have no part in the game if you use packaged virtualenvs. OTOH developer time is expensive. Do you really want to pay your developers to implement functionality that a more recent version of a package has already implemented? A good example is IPv6 support in Twisted. It’s getting implemented right now but I guess (and hope) that I’ll need it sooner than it lands in major distros (please no “lol ipv6” here, it’s just an example and the support is growing).
> Second, DO NOT use virtualenv. It fixes the symptoms (Python's packaging system has many shortcomings such as inability to uninstall recursively, poor dependency management, lack of pre and post install scripts, etc.), but not the problem. Instead, use distro-appropriate packages.
I’m not sure what your problem is, but mine is that I don’t want to develop against a moving target and need to run apps with contradicting dependencies on the same host.
That’s how I started using virtualenv years ago BTW, I’m not talking ivory tower here.
> Integrate your app into the system.
Yes. And I prefer supervisor for that. If your prefer rc.d scripts, be my guest.
> You also get the ability to very nicely manage dependencies and a clean separation between code and configuration.
I don’t get this one TBH.
> Lastly, DO use apache + mod_wsgi. It is fast, stable, widely supported and well tested.
And nginx + uwsgi/gunicorn aren’t?
> If apache feels like a ball of mud, take the time to understand how to cut it down to a minimum and configure it properly.
I know Apache pretty well, because we’re running thousands of customers on them. I’ve already written modules for it and been more than once in it‘s guts. And my impression is not a good one.
My point was to look around before you settle. If you think Apache is da best, knock yourself out. However stuff I see daily on IRC lets me think that it isn’t very unproblematic.
I’m not going to start a “vi vs. emacs”-style holy war here. That’s why I wrote “shop around before you settle” and not ”don’t ever use Apache”.
> When it comes to infrastructure, making boring choices leads to predictable performance and less headaches more often than not (at least in my experience).
Absolutely. nginx is way past the “new and hacky” state though.
This guy seems to be of the opinion that the software should be completely isolated from the deployment operating system.
I know that's a common view and wrapping as much of the site as possible up in a virtualenv certainly has a lot of advantages. But ultimately, your software is going to have to interact with the OS, at some level, otherwise, why do you even have an OS? So the question is: where do you draw the line? He seems to draw it further down the stack than most people (no system python, for instance) but he doesn't give his opinion on, for instance, using the system postgresql.
Anyway, I personally would draw the line further up the stack than him, but take things on a case-by-case basis, and I don't really consider it an "anti-pattern."
With regards to fabric vs. puppet, I understand the advantages of puppet when you have a complicated, hetrogenous deployment environment. But the majority of projects I've worked on have the operations model of a set of identically-configured application servers back-ended against a database server. For this configuration, what does puppet give you? If the author's argument is that the site may eventually outgrow that model, well, I can see puppet becoming necessary, but why not cross that bridge when you get to it?
I think there's an exageration as well, today the trend seems to be "use nothing by the distro"
Ok, sure, MongoDB still changes a lot between versions, in this case you should use the latest version.
But stop there. Especially if you're paying for support (like RHEL)
There should be a good reason for you to compile Apache / MySQL / PostgreSQL / Python. Otherwise, use the distro version. One (common) exception would be "we need Python 2.7 but this ships only 2.6"
Most of the "just download and compile" have no idea of the work that goes behind Linux distributions to ship these packages.
Yes, I'm sure you're going to read all security advisories and recompile all your stack every X days instead of running apt/yum upgrade
If you use puppet/chef for the whole stack, you gain the ability of just starting a new machine and in a couple of minutes having it configured in the exact same way as all the others.
With fabric and similar systems it's a bit harder. Basically you'd have to write your scripts exactly the same way you'd write a puppet/chef recipe: "make sure this is configured that way, make sure that is installed", etc. (or do migration steps) It's very different from fabric's "do this, do that" approach. Unless you run fabric on every single host after you make every change, some of your infrastructure will be lagging behind.
For example, what do you do when you create a new server, or do an upgrade that involves different dependencies? Run a fabric script that migrates from state X to Y? What happens to new machines then? How do you make sure they're in the same state?
I found chef a very good solution even if I have a single server to manage. No need to think about how it was configured before. Migrating to another provider? Just migrate the data, point the server at chef, done.
Point of fact, he does give his opinion on the postgresql issue: "We also have to compile our own Apaches and MySQLs because we need that fine-grained control."
But that's besides the point. I don't think he's arguing that software should be completely isolated form the deployment operating system. That would be absurd, since, as you pointed out, software has to interact with the OS at some level, i.e., to manage system resources. Just because the OS ships with a bunch of packages with specific versions doesn't mean you have to use them. And what I think the OP is saying is that to make your applications portable and easily deployable, you shouldn't.
I draw the line at system libraries and long established system services email, cron, syslog, dns, etc.
I always want to compile my full stack; DB, network servers, language.
> isolated
Perhaps a better term would be "decoupled"?
I am glad this is working for the OP, but pushing virtualenv and "self-contained" apps as the one solution is a diservice to the community. There are valid reasons to rely on your OS, assuming you have an homogenous deployment target (same OS, maybe different versions):
- lots of people argue for virtualenv because some versions may be incompatible. The problem here is the lack of backward compatibility of packages, and frankly, if you need to rely on packages which change API willingnily betwen e.g. 1.5 and 1.6, or if each of your service depends on a different version of some library, you have bigger problems anyway.
- any sufficiently complex deployment will depend on things that are not python, at which point you need a solution that integrates multiple languages. That is, you re-creating what a distribution is all about.
- virtualenv relies on sources, so if some of your dependences are in C, every deploy means compilation
- I still have no idea how security is handled when you put everything in virtualenv
See also http://bytes.com/topic/python/answers/841071-eggs-virtualenv...
> pushing virtualenv and "self-contained" apps as the one solution is a diservice to the community.
Wow. :(
> There are valid reasons to rely on your OS, assuming you have an homogenous deployment target (same OS, maybe different versions):
I’d love to hear them.
> lots of people argue for virtualenv because some versions may be incompatible. The problem here is the lack of backward compatibility of packages, and frankly, if you need to rely on packages which change API willingnily betwen e.g. 1.5 and 1.6, or if each of your service depends on a different version of some library, you have bigger problems anyway.
Well, you said there are possibilities of problems but that they shouldn’t matter in an ideal world. Maybe you’re okay to take the chances but I’m not. Every code I deploy has been tested rigorously against a certain set of versions and that is the only combination of dependencies I’m willing to consider “working”. UnitTests with different dependencies are just as worthless like integration/functional tests against sqllite instead of the same DB type as in production.
There’s even the possibility that your code works because of a bug and when that one gets fixed, you app goes south because of some weird side-effect.
> any sufficiently complex deployment will depend on things that are not python, at which point you need a solution that integrates multiple languages. That is, you re-creating what a distribution is all about.
I’m not sure if I understand what you mean, but yes if you want to use certain features outside the Python ecosystem, you’ll have to buckle up and package them yourself too. “We can’t do that, package XYZ is missing/too old.” isn’t really a good excuse to not do something that is important/good for your business. And that’s one of the main points of the article.
> virtualenv relies on sources, so if some of your dependences are in C, every deploy means compilation
That’s wrong if you go the way described: The virtualenv is packaged with the code. Build tools don’t belong on production servers.
> I still have no idea how security is handled when you put everything in virtualenv
Just as everywhere else. If you think it’s okay to tell customers that their data has been hacked because debian was to slow to issue a fix, be my guest. We can’t afford that. What happens on my servers security wise is _my_ responsibility and using ancient versions of Python libraries just to be able to blame others for FUBARs is not a solution in my book.
I disagree. IMO dynamic load libraries was a known bad solution before they were made (dll hell). Plenty of exploits have come from them, plenty of horror stories, etc. If you have a nice distro anyway, upgrading a given library that everyone packages should be doable.
Windows still uses shared libraries but at least they invented the GAC so applications can specify exactly which version of a library they work with and the installer will install that version if it's not present.
Using tmux is a Python daemon antipattern? And then "there's so much wrong about this approach" that he doesn't bother explaining why? Isn't that why we are reading the article: because we want to know why?
If the author is trying to convince people to change their habits, he is doing a crummy job. He comes across as elitist and "if you don't do it my way you're wrong".
He's talking about creating /etc/init.d scripts that do something like:
screen python manage.py gunicorn &
That is an anti-pattern. Granted he didn't really explain it so well.
I’m sorry if that felt to you like that. I’ll consider rewording it.
update I added some more context. I would never spit on my beloved tmux. :)
Don’t run your daemons in a tmux/screen
Wow, I always though of myself as an idiot for doing this. But that is for some not yet launched thing. Who on earth does this for a production website?
The ability of Go to produce a single, self-contained executable is one of the biggest advantages it has over the "scripting" languages. It makes deployment so much simpler.
Virtualenv is a half solution and a hack. Use vagrant and VMs. There's a whole sea of libs and software that isn't "versioned" by pip/virtualenv.
supervisord is the wrong solution. It answers the wrong question (is the process running). It's worse than useless in that it has given false positives. The right question is (is the process responding correctly). Use monit or something else that actually does what's needed.
Vagrant ist nice for testing but I’m not going to deploy services to VirtualBox (we use kvm for that). Of course there are dependencies outside of the Python ecosystem but their influence proved to be negligible till now. YMMV.
supervisor is not a an alternative to monitoring, I never claimed that. But that’s a whole different story.
virtualenv isn't just used for testing, though. it's widely used to isolate applications' python environments/dependencies from one another.
Why would you want to virtualise an entire system when your dependencies are restricted to a bunch of Python modules?
Just a thank you for writing a positive, easy to follow overview with links to more in-depth information. I love when people boil down experience and serve it without a side dish of attitude.