ansible roles

Automating My Infrastructure with Ansible and Gitlab CI: Part 2 – Deploying Stuff with Roles

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In the first post of this series, I got started with Ansible running in Gitlab CI. This involved setting up the basic pipeline, configuring the remote machines for use with our system and making a basic playbook to perform package upgrades. In this post we’re going to build on top of this to create a re-usable Ansible role to deploy some software and configuration to our fleet of servers. We will do this using the power of Ansible roles.

In last week’s post I described my monitoring system, based on checkmk. At the end of the post I briefly mentioned that it would be great to use Ansible to deploy the checkmk agent to all my systems. That’s what I’m going to describe in this post. The role I’ve created for this deploys the checkmk agent from the package download on my checkmk instance and configures it to be accessed via SSH. It also installs a couple of plugins to enable some extra checks on my systems.

A Brief Aside: ansible-lint

In my previous post I set up a job which ran all the playbooks in my repository with the --check flag. This performs a dry run of the playbooks and will alert me to any issues. In that post I mentioned that all I was really looking for was some kind of syntax/sanity checking on the playbooks and didn’t really need the full dry run. Several members of the community stepped forward to suggest ansible-lint – thanks to all those that suggested it!

I’ve now updated my CI configuration to run ansible-lint instead of the check job. The updated job is shown below:

This is a pretty basic use of ansible-lint. All I’m doing is running it on all the playbooks in my playbooks directory. I do skip a single rule (403) with the -x argument. The rule in question is about specifying latest in package installs, which conflicts with my upgrade playbook. Since I’m only tweaking this small thing I just pass this via the CLI rather than creating a config file.

I’ve carried the preflight jobs and the ansible-lint job over to the CI configuration for my new role (described below). Since this is pretty much an exact copy of that of my main repo, I’m not going to explain it any further.

Creating a Base Role

I decided that I wanted my roles self contained in their own git repositories. This keeps everything a bit tidier at the price of a little extra complexity. In my previous Ansible configuration I had all my roles in the same repo and it just got to be a big mess after a while.

To create a role, first initialise it with ansible-galaxy. Then create a new git repo in the resulting directory:

I actually didn’t perform these steps and instead started from a copy of the old role I had for this in my previous configuration. This role has been tidied up and expanded upon for the new setup.

The ansible-galaxy command above will create a set of files and directories which provide a skeleton role. The first thing to do is to edit the README.md and meta/main.yml files for your role. Just update everything to suit what you are doing here, it’s pretty self explanatory. Once you’ve done this all the files can be added to git and committed to create the first version of your role.

Installing the Role

Before I move on to exactly what my role does, I’m going to cover how we will use this role in our main infrastructure project. This is done by creating a requirements.yml file which will list the required roles. These will then be installed by passing the file to ansible-galaxy. Since the installation tool can install from git we will specify the git URL as the installation location. Here are the contents of my requirements.yml file:

Pretty simple. In order to do the installation all we have to do is run the following command:

This will install the required Ansible roles to the playbooks/roles directory in our main project, where our playbooks can find them. The --force flag will ensure that the role always gets updated when we run the command. I’ve added this command in the before_script commands in the CI configuration to enable me to use the role in my CI jobs.

Now the role will be installed where we actually need it. However, we are not yet using it. I’ll come back to this later. Let’s make the role actually do something first!

What the Role Does

The main behaviour of the role is defined in the tasks/main.yml file. This file is rather long, so I won’t reproduce this here. Instead I’ll ask you to open the link and follow along with my description below:

  • The first task creates a checkmk user on the target system. This will be used by checkmk to log in and run the agent.
  • The next task creates a .ssh directory for the checkmk user and sets it’s permissions correctly.
  • Next we create an authorized_keys file for the user. This uses a template file which will restrict what the key can do. The actual key comes from the checkmk_pub_key variable which will be passed in from the main project. The template is as follows:
  • Next are a couple of tasks to install some dependent packages for the rest of the role. There is one task for Apt based systems and another for Yum based systems. I’m not sure if the monitoring-plugins package is actually required. I had it in my previous role and have just copied it over.
  • The two tasks remove the xinetd package on both types of system. Since we are accessing the agent via SSH we don’t need this. I was previously using this package for my agent access so I want to make sure it is removed. This behaviour can be disabled by setting the checkmk_purge_xinetd variable to false.
  • The next task downloads the checkmk agent deb file to the local machine. This is done to account for some of the remote servers not having direct access to the checkmk server. I then upload the file in the following task. The variables checkmk_server, checkmk_site_name and checkmk_agent_deb are used to specify the server address, monitoring instance (site) and deb file name. The address and site name are designed to be externally overridden by the main project.
  • The next two tasks repeat the download and upload process for the RPM version of the agent.
  • We then install the correct agent in the next two tasks.
  • The following task disables the systemd socket file for the agent to stop it being accessible over an unencrypted TCP port. Right now I don’t do this on my CentOS machines because they are too old to have systemd!
  • The final few tasks get in to installing the Apt and Docker plugins on systems that require it. I follow the same process of downloading then uploading the files and make them executable. The Docker plugin requires that the docker Python module be installed, which we achieve via pip. It also requires a config file, which as discussed in my previous post needs to be modified. I keep my modified copy in the repository and just upload it to the correct location.

The variables that are used in this are specified in the vars/main.yml and defaults/main.yml files. The default file contains the variables that should be overridden externally. I don’t specify a default for the SSH public key because I couldn’t think of a sensible value, so this at least must be specified for the role to run.

With all this in place our role is ready to go. Next we should try that from our main project.

Applying the Role

The first thing to do is to configure the role via the variables described above. I did this from my hosts.yml file which is encrypted, but the basic form is as follows:

The public key has to be that which will be used by the checkmk server. As such the private key must be installed on the server. I’ll cover how to set this up in checkmk below.

Next we have the playbook which will apply our role. I’ve opted to create a playbook for applying common roles to all my systems (of which this is the first). This goes in the file playbooks/common.yml:

This is extremely basic, all it does is apply the checkmk_agent role to all servers.

The corresponding CI job is only marginally more complex:

With those two in place a push to the server will start the pipeline and eventually deploy our role to our servers.

ansible roles
Our updated CI pipeline showing the ansible-lint job and the new common-roles job

Configuring Checkmk Agent Access via SSH

Of course the deployment on the remote servers is only one side of the coin. We also need to have our checkmk instance set up to access the agents via SSH. This is documented pretty well in the checkmk documentation. Basically it comes down to putting the private key corresponding to the public key used earlier in a known location on the server and then setting up an “Individual program call instead of agent access” rule in the “Hosts and Service Parameters” page of WATO.

I modified the suggested SSH call to specify the private key and user to use. Here is the command I ended up using in my configuration.

When you create the rule you can apply it to as many hosts as you like. In my setup this is all of them, but you should adjust as you see fit.

ansible roles
The checkmk WATO rule screen for SSH agent access

Conclusion

If you’ve been following along you should now be able to add new hosts to your setup (via hosts.yml) and have the checkmk agent deployed on them automatically. You should also have an understanding of how to create reasonably complex Ansible roles in external repositories and how to use them in your main Ansible project.

There are loads of things about roles that I haven’t covered here (e.g. handlers). The best place to start learning more would be the Ansible roles documentation page. You can then fan out from there on other concepts as they arise.

Next Steps

So far on this adventure I’ve tested my playbooks and roles by just making sure they work against my servers (initially on a non-critical one). It would be nice to have a better way to handle this and to be able to run these tests and verify that the playbook is working from a CI job. I’ll be investigating this for the next part of this series.

The next instalment will probably be delayed by a few weeks. I have something else coming which will take up quite a bit of time. For my regular readers, there will still be blog posts – they just won’t be about Ansible or CI. This is probably a good thing, I’ve been covering a lot of CI stuff recently!

As always please get in contact if you have any feedback or improvements to suggest, or even if you just want to chat about your own Ansible roles.

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checkmk docker container

Monitoring All The Things with checkmk

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Once your number of connected devices grows to a certain size, it becomes difficult to keep track of them all manually. At this point you’re going to want to turn to software to do this job for you. Network monitoring software fills this need nicely. The old stable Nagios used to be my go to for this. However, I switched to checkmk in the last couple of years and have found it quite superior. I’ve recently been doing some maintenance and upgrades to my monitoring setup, so now was a good time to write it up.

Checkmk is an Open Source infrastructure and application monitoring tool. It will keep track various attributes of your networked devices and alert you if they fall outside of pre-programmed thresholds. At its core it wraps Nagios, but provides a nicer UI and GUI configuration tool. checkmk also supports autodiscovery of services and checks to be performed on each system. This means you can spin up a monitoring system with great coverage in less than half the time you would spend fiddling around with a Nagios configuration.

Monitoring vs. Metrics

I’m going to take a little time to discuss the modern trend towards “metrics” based monitoring and how it relates to more traditional monitoring approaches. Modern metrics based systems such as Prometheus and Influxdb collect a series of aggregated data points about a running system. Typically these are written to a time series database (Influxdb actually is purely a time series database and requires external data collection tools). This data would then be used to feed some graphing/dashboarding tool, such as Grafana and also to generate alerts.

This is a different approach to traditional monitoring. To my mind metrics gathering is more passive. The system is only asking what the other systems (or typically only the applications on those systems) know about themselves. It is not actually probing the network to check that things are working. Monitoring systems not only collect data from systems, but actually probe the network to create data, for example whether a given service is responding or not.

The metrics gathering approach works well if all you care about are the applications. Obviously the application knows everything about itself, so why not ask it? It’s particularly popular in cloud environments where someone else is caring about the underlying infrastructure. Anywhere you care about physical infrastructure you’d probably be better off with a monitoring system first. Of course, this doesn’t preclude adding a metrics system later!

I think its important not to get these tools mixed up, they serve different purposes, even if there is some overlap.

Let’s Start Monitoring

I’ve had checkmk installed inside an LXD container for some time. In that time it’s been running pretty much flawlessly and alerting me to issues with my network as they come up. I recently decided it was time for an update, since I was still running 1.4.x and 1.5 had been out for a while. In the process I thought I’d move it into Docker, as I’ve been moving everything else. However, I ran into some issues with that.

I had several issues moving my configuration to the new server and getting it to run in the Docker container. Most of these could have been solved if I’d migrated the configuration to the new version (described below) before moving it. I did hit one show stopper issue though. This came about because my Docker data volumes are stored on NFS. Basically it looks like NFS doesn’t support file locking very well. This causes checkmk to throw “Bad file descriptor” errors all over the place.

checkmk nfs error
Oops, looks like checkmk doesn’t like it’s sites directory on NFS

In the end I decided to stick with my LXD container for this system. Eventually this will be migrated to an LXC container when I switch the host server over to Proxmox. The Docker setup is not actually recommended for a full monitoring install anyway, so I don’t feel too bad about this.

This is all a long winded way of saying, go and follow the Linux installation instructions if you are installing checkmk from scratch!

Upgrading My Configuration

Since I already had an existing system I just updated it by installing the new version. In the process checkmk 1.6 was released (good timing!), so I actually did this twice. To do the update I basically just downloaded the latest .deb file and installed it with dpkg -i.

It should be noted that this won’t overwrite your current install. There is a good reason for this, since checkmk has a configuration migration step which must be performed. This can be done using the omd tool. The steps to do so look like this:

Assuming that all went OK, you’re good to start actually monitoring other systems. We’ll cover the things I monitor in the next few sections.

Monitoring Standard Linux Systems

This is the easy one and pretty much standard fare for any monitoring system. Just install the checkmk agent for your distribution by following the official instructions and off you go. When you add a new host via WATO (the configuration GUI) checkmk will auto-discover as many services as it can for you. There are also a whole load of plugins that can be deployed to monitor other services.

checkmk linux server
Some of the service checks running against “eomer” my home automation Docker host

In my system, Linux machines are the majority of the hosts. This includes physical host machines, VMs, LXC/LXD containers and Raspberry Pis (since these are just Debian machines really). The only thing I haven’t had much luck with are my Libreelec machines. This seems to be because Libreelec doesn’t include a shell capable of running the agent script. I’ve been wondering if running the agent in a sufficiently privileged Docker container would work. However for now I’m just monitoring them externally (see “Monitoring Other Devices” below).

Monitoring pfSense

Since pfSense is really just FreeBSD underneath the checkmk BSD agent works fine with it. pfSense also supports SNMP out of the box. Therefore you can get more monitoring coverage by using an Agent+SNMP approach. There is a great tutorial over at Open School Solutions, which is what I followed to set all that up.

checkmk pfsense
pfSense will report the status of all its network interfaces among its checks

Monitoring OpenWRT Devices

OpenWRT devices can be monitored just like Linux machines. However you will need to install the OpenWRT specific agent from the agents page of your checkmk install. The agent can be run via either xinetd or SSH just as on a standard Linux machine.

OpenWRT devices will also return some extra information over SNMP if mini_snsmpd is installed on them. This makes the same Agent+SNMP approach adopted for pfSense desirable.

Monitoring Docker Containers

This one is new to me since I’ve just set it up after updating to the new version. The basic idea here is that you set up monitoring on the Docker host as you would a standard Linux machine. However, you also install the mk_docker.py plugin. This will do two things. Firstly it will expose a load of Docker checks on the host the next time you run service discovery. These by themselves are pretty useful. Secondly it will allow you to add each Docker container on the host as a host in it’s own right. The check data for the Docker container host is piggybacked from the agent connection to its Docker host.

At first I thought this was going to be pretty unwieldy, since you have to manually add a host entry for each Docker container. However, checkmk provides us with some tools to make this easier, which I’ll cover below.

Before you finish the setup on the Docker host, I’d recommend that you set the container_id variable in the /etc/checkmk/docker.cfg config file to name. This will allow you to add your container hosts to checkmk by name rather than by hex ID, which is much more human readable. It also avoids the situation where the hex ID changes if the container is destroyed and re-created. This obviously happens during an update of the container.

Adding Docker Container Hosts Quickly

checkmk wato folder
Setting up a host folder in WATO allows you to apply the same initial options to a bunch of hosts quickly

The next thing to do is to create a directory in WATO. Adding a host to a directory automatically populates the host with the configuration template used when the directory was created. This makes it super quick to just run through adding hosts with the same configuration such as our Docker containers.

The third thing to do is to create a new Host Group for your Docker containers. In this way you can easily see separate listings of your containers and other hosts on the monitoring dashboards.

checkmk hostgroup
Creating a host group for my Docker contains allow me to view just the statuses of the containers

With these things in place I’m finding the Docker container monitoring pretty useful in my fairly static environment. Due to the manual steps involved it’s really not going to work in a highly dynamic environment, but it works for my needs.

checkmk docker container
My Gotify container is unhappy – because I artificially stopped it for the screenshot!

Monitoring Windows Machines

Obviously checkmk also has an agent for Windows, so you can monitor those machines too. If you have any. I don’t, so I can’t comment on how well it works!

Monitoring Other Devices

For monitoring other devices that don’t support any of the available agents, you’re pretty much limited to external probing. With this you can get basic information on whether the device is up or down (via ping) and can check the availability of services on any open ports via manual checks.

Manual checks are in fact useful against any of the systems listed above as an external verification that a service is responding. As a minimum I typically implement an SSH check as well as HTTP checks on any open web services.

I have this approach deployed against several devices on my network including the two Libreelec devices mentioned above, my HDHomeRun and various IoT devices. It works pretty well – especially as the usual problem with these devices is that someone has unplugged them!

Conclusion

I hope this has given you a glimpse into my monitoring setup. It’s impossible to describe every part of it in full detail so I’ve opted for presenting only an overview here. Even after nearly two years I’m still adding and changing stuff on this system, so I may write up some of the more interesting details in future.

I’m really happy with my choice of checkmk to drive my monitoring system. It’s a nice blend of the reliability and stability of Nagios, with a layer of UI which makes it much easier to get a fully featured system. The recent upgrades have provided some useful features and it’s great to see it under such active development!

Next Steps

I still have some corners of my network where my monitoring setup doesn’t cover. Mainly just through lack of time to get it all set up. I’ll be looking to Ansible to help with this soon.

I’d also like to add some kind of metrics gathering system, probably Influxdb. This will be for Home Assistant data and metrics from my Traefik proxies (as well as anything else I can feed to it). I’d also like to round out the trifecta of observation systems with a log storage/aggregation system. I just wish there was something more lightweight than an ELK stack!

If you have any comments or improvements to my setup, as always, let me know in the feedback channels. I’m also interested in how others are handling this, so get in touch and let me know.

If you liked this post and want to see more, please consider subscribing to the mailing list (below) or the RSS feed. You can also follow me on Twitter. If you want to show your appreciation, feel free to buy me a coffee.