Amazon Linux AMI : Let’s Encrypt : ImportError: No module named interface

Let’s Encrypt has only experimental support for the Amazon Linux AMI, so it’s kind of expected to have issues once in a while.   Here’s one I came across today:

# /opt/letsencrypt/certbot-auto renew
Creating virtual environment...
Installing Python packages...
Installation succeeded.
Traceback (most recent call last):
File "/root/.local/share/letsencrypt/bin/letsencrypt", line 7, in <module>
from certbot.main import main
File "/root/.local/share/letsencrypt/local/lib/python2.7/dist-packages/certbot/", line 12, in <module>
import zope.component
File "/root/.local/share/letsencrypt/local/lib/python2.7/dist-packages/zope/component/", line 16, in <module>
from zope.interface import Interface
ImportError: No module named interface

My first though was to install the system updates. It looks like something is off in the Python-land. But even after the “yum update” was done, the issue was still there. A quick Google search later, thanks to the this GitHub issue and this comment, the solution is the following:

pip install pip --upgrade
pip install virtualenv --upgrade
virtualenv -p /usr/bin/python27 venv27

Running the renewal of the certificates works as expected after this.

P.S.: I wish we had fewer package and dependency managers in the world…

Install Ansible 2.0+ on Amazon AMI

Today, while upgrading some of my Ansible roles I’ve hit the problem.  Some of the newer roles require Ansible 2.0.  My Amazon AMI machine that runs the playbooks was still on version 1.9.  EPEL repository doesn’t seem to have the newer Ansible version yet.  Gladly, Google brough in this StackOverflow thread, which suggested installing Ansible with pip, not with yum.  This helped a lot:

rpm -e ansible
pip install ansible

It actually brought in Ansible v2.2 (see also Ansible v2.1), which is even better.

Amazon Linux AMI 2016.09

amazon ami 2016.09

AWS Blog lets us know that Amazon Linux AMI 2016.09 is now available.  It comes with a variety of updates, such as Nginx 1.10, PHP 7, and PostgreSQL 9.5 and Python 3.5.  Another thing that got quite a bit of improvement is the boot time of the Amazon Linux AMI instances.  Here’s a comparison chart:


Read about all the changes in the release notes.

P.S.: I’m still stuck with Amazon AMI on a few of my instances, but in general I have to remind all of you to NOT use the Amazon AMI.  You’ve been warned.

Forcing Amazon Linux AMI compatibility with CentOS in Ansible

One of the things that makes Ansible so awesome is a huge collection of shared roles over at Ansible Galaxy.  These bring you best practices, flexible configurations and in general save hours and hours of hardcore swearing and hair pulling.

Each role usually supports multiple versions of multiple Linux distributions.  However, you’ll find that the majority of the supported distributions are Ubuntu, Debian, Red Hat Enterprise Linux, CentOS, and Fedora.  The rest aren’t as popular.

Which brings me to the point with Amazon Linux AMI.  Amazon Linux AMI is mostly compatible with CentOS, but it uses a different version approach, which means that most of those Ansible roles will ignore or complain about not supporting Amazon AMI.

Here is an example I came across yesterday from the dj-wasabi.zabbix-server role.  The template for the Yum repository uses ansible_os_major_version variable, which is expected to be similar to Red Hat / CentOS version number – 5, 6, 7, etc.  Amazon Linux AMI’s major version is reported as “NA” – not available.   That’s probably because Amazon Linux AMI versions are date-based – with the latest one being 2016.03.

name=Zabbix Official Repository - $basearch
baseurl={{ zabbix_version }}/rhel/{{ ansible_distribution_major_version }}/$basearch/

Officially, Amazon Linux AMI is not CentOS or Red Hat Enterprise Linux.  But if you don’t care about such little nuances, and you are brave enough to experiment and assume things, than you can make that role work, by simply setting the appropriate variables to the values that you want.

First, here is a standalone test.yml playbook to try things out:

- name: Test
  hosts: localhost
  - set_fact: ansible_distribution_major_version=6
    when: ansible_distribution == "Amazon"
  - debug: msg={{ ansible_distribution_major_version }}

Let’s run it and look at the output:

$ ansible-playbook test.yml

PLAY [Test] *******************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [set_fact ansible_distribution_major_version=6] *************************
ok: [localhost]

TASK: [debug msg={{ ansible_distribution_major_version }}] ********************
ok: [localhost] => {
  "msg": "6"

PLAY RECAP ********************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=0

So far so good.  Now we need to integrate this into our playbook in such a way that the variable is set before the third-party role is executed.  For that, we’ll use pre_tasks.  Here is an example:

- name: Zabbix Server
  hosts: zabbix.server
  sudo: yes
    - set_fact: ansible_distribution_major_version=6
      when: ansible_distribution == "Amazon" and ansible_distribution_major_version == "NA"
    - role: dj-wasabi.zabbix-server

A minor twist here is also checking if the major version is not set yet. You can skip that, or you can change it, for example, to examine the Amazon Linux AMI version and set corresponding CentOS version.

Let’s Encrypt on CentOS 7 and Amazon AMI

The last few weeks were super busy at work, so I accidentally let a few SSL certificates expire.  Renewing them is always annoying and time consuming, so I was pushing it until the last minute, and then some.

Instead of going the usual way for the renewal, I decided to try to the Let’s Encrypt deal.  (I’ve covered Let’s Encrypt before here and here.)  Basically, Let’s Encrypt is a new Certification Authority, created by Electronic Frontier Foundation (EFF), with the backing of Google, Cisco, Mozilla Foundation, and the like.  This new CA is issuing well recognized SSL certificates, for free.  Which is good.  But the best part is that they’ve setup the process to be as automated as possible.  All you need is to run a shell command to get the certificate and then another shell command in the crontab to renew the certificate automatically.  Certificates are only issued for 3 months, so you’d really want to have them automatically updated.

It took me longer than I expected to figure out how this whole thing works, but that’s because I’m not well versed in SSL, and because they have so many different options, suited for different web servers, and different sysadmin experience levels.

Eventually I made it work, and here is the complete process, so that I don’t have to figure it out again later.

We are running a mix of CentOS 7 and Amazon AMI servers, using both Nginx and Apache.   Here’s what I had to do.

First things first.  Install the Let’s Encrypt client software.  Supposedly there are several options, but I went for the official one.  Manual way:

# Install requirements
yum install git bc
cd /opt
git clone letsencrypt

Alternatively, you can use geerlingguy’s lets-encrypt-role for Ansible.

Secondly, we need to get a new certificate.  As I said before, there are multiple options here.  I decided to use the certonly way, so that I have better control over where things go, and so that I would minimize the web server downtime.

There are a few things that you need to specify for the new SSL certificate.  These are:

  • The list of domains, which the certificate should cover.  I’ll use and here.
  • The path to the web folder of the site.  I’ll use /var/www/vhosts/
  • The email address, which Let’s Encrypt will use to contact you in case there is something urgent.  I’ll use here.

Now, the command to get the SSL certificate is:

/opt/letsencrypt/certbot-auto certonly --webroot --email --agree-tos -w /var/www/vhosts/ -d -d

When you run this for the first time, you’ll see that a bunch of additional RPM packages will be installed, for the virtual environment to be created and used.  On CentOS 7 this is sufficient.  On Amazon AMI, the command will run, install things, and will fail with something like this:

WARNING: Amazon Linux support is very experimental at present...
if you would like to work on improving it, please ensure you have backups
and then run this script again with the --debug flag!

This is useful, but insufficient.  Before you can run successfully, you’ll also need to do the following:

yum install python26-virtualenv

Once that is done, run the certbot command with the –debug parameter, like so:

/opt/letsencrypt/certbot-auto certonly --webroot --email --agree-tos -w /var/www/vhosts/ -d -d --debug

This should produce a success message, with “Congratulations!” and all that.  The path to your certificate (somewhere in /etc/letsencrypt/live/ and its expiration date will be mentioned too.

If you didn’t get the success message, make sure that:

  • the domain, for which you are requesting a certificate, resolves back to the server, where you are running the certbot command.  Let’s Encrypt will try to access the site for verification purposes.
  • that public access is allowed to the /.well-known/ folder.  This is where Let’s Encrypt will store temporary verification files.  Note that the folder starts with dot, which in UNIX means hidden folder, which are often denied access to by many web server configurations.

Just drop a simple hello.txt to the /.well-known/ folder and see if you can access it with the browser.  If you can, then Let’s Encrypt shouldn’t have any issues getting you a certification.  If all else fails, RTFM.

Now that you have the certificate generated, you’ll need to add it to the web server’s virtual host configuration.  How exactly to do this varies from web server to web server, and even between the different versions of the same web server.

For Apache version >= 2.4.8 you’ll need to do the following:

SSLEngine on
SSLCertificateKeyFile /etc/letsencrypt/live/
SSLCertificateFile /etc/letsencrypt/live/

For Apache version < 2.4.8 you’ll need to do the following:

SSLEngine on
SSLCertificateKeyFile /etc/letsencrypt/live/
SSLCertificateFile /etc/letsencrypt/live/
SSLCertificateChainFile /etc/letsencrypt/live/

For Nginx >= 1.3.7 you’ll need to do the following:

ssl_certificate /etc/letsencrypt/live/;
ssl_certificate_key /etc/letsencrypt/live/;

You’ll obviously need the additional SSL configuration options for protocols, ciphers and the like, which I won’t go into here, but here are a few useful links:

Once your SSL certificate is issued and web server is configured to use it, all you need is to add an entry to the crontab to renew the certificates which are expiring in 30 days or less.  You’ll only need a single entry for all your certificates on this machine.  Edit your /etc/crontab file and add the following (adjust for your web server software, obviously):

# Renew Let's Encrypt certificates at 6pm every Sunday
0 18 * * 0 root (/opt/letsencrypt/certbot-auto renew && service httpd restart)

That’s about it.  Once all is up and running, verify and adjust your SSL configuration, using Qualys SSL Labs excellent tool.

Do Not Use Amazon Linux

I came across “Do Not Use Amazon Linux” opinion on Ex Ratione.  I have to say that I mostly agree with it.  When I initially started using Amazon Web Services, I assumed (due to time constraints mostly) that Amazon Linux was a close derivative of CentOs and I opted for that.  For the majority of things that affect applications in my environment that holds true, however it’s not all as simple as it sounds.

There are in fact differences that have to be taken into account.  Some of the configuration issues can be abstracted with the tools like Puppet (which I do use).  But not all of it.   I’ve been bitten by package names and version differences (hello PHP 5.3, 5.4, and 5.5; and MySQL and MariaDB) between Amazon AMI and CentOS distribution.  It’s an absolute worst when trying to push an application from our testing and development environments into the client’s production environment.  Especially when tight deadlines are involved.

One of the best reasons for CentOS is that developers can easily have their local environments (Vagrant anyone?) setup in an exactly the same way as test and production servers.