Robin Bowes

We've all run into problems like this: $ echo 12000 > /proc/sys/vm/dirty_writeback_centisecs -bash: /proc/sys/vm/dirty_writeback_centisecs: Permission denied The command fails because the target file is only writeable by root. The fix seems obvious and easy: $ sudo echo 12000 > /proc/sys/vm/dirty_writeback_centisecs -bash: /proc/sys/vm/dirty_writeback_centisecs: Permission denied Huh? It still fails. What gives? The reason it fails is that it is the shell that sets up the re-direction before running the command under sudo. The solution is to run the whole pipeline under sudo. There are several ways to do this: echo 'echo 12000 > /proc/sys/vm/dirty_writeback_centisecs' | sudo sh sudo sh -c 'echo 12000 > /proc/sys/vm/dirty_writeback_centisecs' echo 12000 | sudo tee /proc/sys/vm/dirty_writeback_centisecs This is fine for simple commands, but what if you have a complex command that already includes quotes and shell meta-characters? Here's what I us...

Volcane recently asked in ##infra-talk on Freenode if anyone knew of " some little tool that can be used in a cronjob for example to noop the the real task if say load avg is high or similar?" I came up with the idea to use nagios plugins. So, for example, to check load average before running a task: /usr/lib64/nagios/plugins/check_load -w 0.7,0.6,0.5 -c 0.9,0.8,0.7 >/dev/null && echo "Run the task here" Substitute the values used for the -w and -c args as appropriate, or use a different plugin for different conditions.

In a previous post , I described how to describe puppet environments, roles, and profiles, as modules and how to use r10k and librarian-puppet to deploy them. One possible problem with deploying to the puppet environment directory directly is that the librarian-puppet run can take some time and there is a possibility that puppet may attempt to compile a catalogue in an incomplete or inconsistent environment. One way to overcome this is to deploy the environments into a new directory, create a symlink, and move the symlink atomically into place . This would look something like this: cd /etc/puppet/envs# create a new dir under /etc/puppet/envs - I use a timestamp in the name so I know when it was createdNEW_ENV_DIR=$(mktemp --directory envs.$(date -Isec).XXX")cd /etc/puppet# use r10k deploy the environments into the new dirPUPPETFILE_DIR="envs/${NEW_ENV_DIR}" r10k puppetfile install# loop over all the environments and use librarian-puppet to deploy all the roles/pro...

By treating roles and profiles as puppet modules, we can use  r10k  and  librarian-puppet to manage the deployment of our puppet code into our puppet environements. I shall assume that puppet is configured to use to use directory environments and that the environment path is $confdir/environments (ie. the default location). I also assume that both r10k and librarian-puppet are installed and in the path. You should also understand and embrace the role-profile-module pattern, first described by Craig Dunn  and subsequently by Adrian Thebo  and Gary Larizza . Quoting Gary: Roles abstract profiles Profiles abstract component modules Hiera abstracts configuration data Component modules abstract resources Resources abstract the underlying OS implementation   I find the following points useful to clarify the purpose of each of the layers in this model: Roles, profiles, and component modules can all be implemented as...

We're using puppet + puppetdb in an EC2 environment where nodes come and go quite regularly. We have a custom autosign script that uses ec2 security info to validate the nodes before allowing the autosigning. This is all good, but it can leave a lot of "dead" nodes in puppet, eg. if a bunch of nodes are created by an autoscale policy and then terminated. To get rid of these zombie nodes from puppet/puppetdb we can just use: puppet node deactivate <certname1> <certname2> ... <certnameN> We can query puppetdb to get a list of nodes that have not sent puppet reports for, say, 24 hours. The puppetdb query we need is something like this: 'query=[" where $cutoff_date is a date in ISO8601 format, eg. 2015-03-05T13:39:45+0000 We can use date to generate the cutoff date with something like this: $cutoff_date=$(date -d '-1 day' -Isec) We then plug this into the query string and send it with curl as follows: curl --silent -G 'http://l...

One of my very early frustrations with puppet was that it allows variables to be used when they were undefined. Primarily this bit me by not catching typos in variable names which were often very hard to track down. I was very pleased when Puppetlabs introduced a strict_variables mode which throws an error if a manifest attempts to use an undefined variable. I recently need to check for the existence of a fact. Without strict_variables, this is straight-forward: if $::some_fact {  # do stuff here} If the fact "some_fact" exists, the variable is a non-empty string and evaluates as true in boolean context. If the fact doesn't exist, the variable is an empty string which evaluates as false in boolean context. But, with strict_variables enforced, this throws an error: Error: Undefined variable "::some_fact"; Undefined variable "some_fact" at line ... The solution is to use the getvar function from stdlib : if getvar('::some_fact'...

The team at bitly  has written an http reverse proxy that provides authentication using Google's OAuth2 API . They write about it in a blog post . The proxy is written in Go  but builds to a single, statically-linked executable, ie. there are no complex run-time dependencies, which is great. I've built an RPM for EL7 which also includes a sample systemd unit file, and sample configuration file. Both source and binary RPMs are available in my yum repo . Additionally, I've create a puppet module that installs the RPM, creates a systemd service, and sets up an nginx front end to the proxy service. The module is available from the Puppetforge , and also on github . I'd be interested in any feedback/comments/bug reports/pull requests.