Devops Diary

Howto secure openssh-6.x

Since OpenSSH 6.x came out, a lot of new ciphers where introduced. I was wondering, which ones where the best and what I should use, and I read a few articles on the internet to find out.

I’m certianly not a cryptographer, so if you have any suggestions howto further improve the configuration below, feel free to contact me.

As a general statement, one should avoid ECDSA and use Ed25519 instead, and due to the fixed key length of DSA that ssh-keygen uses, DSA should also be avoided. RSA keys should be at least 2048 bits long, perhaps 4096 bits is the better choice.

conf.d like directories for zsh/bash dotfiles

I don’t like messy dotfiles.

The thought of having tons of random configuration entries in files like my .zshrc really bothers me, so I implemented something that works like a conf.d like directory structure for my shell dotfiles.

I also still use the bash shell in certian situations, and I want a more or less consistent environment, no matter which shell I use (bash, zsh).

With the following setup, it’s possible to have the following:

  • A directory called zshrc.d, which includes multiple, zsh related configuration files.
  • A directory called bashrc.d, including multiple configuration files concerning bash.
  • A directory called rc.d, including configuration items needed by both shells.
  • A directory called login.d, including elements included by .bash_profile resp. .zlogin.

This keeps your dotfiles nice and clean, and also allows you do have additional files on systems where you need them, without them being included on all your systems (e.g. your $GOPATH).

gittree: bash/zsh function to run git commands recursively

I’m using Androids repo tool from time to time when dealing with large groups of git repositories. In most situations, it is too bloated though. Some git “batch” commands I found very useful, like repo status, checking the status of all git repositories recursively.

To mimic this (and other) behaviour in a simple way, I created the following bash/zsh function (put this in your .bashrc or .zshrc, or another file where you define functions in your dotfiles)

Nested if workaround for Nginx to allow a specific ip address access to a disabled site

When doing maintenance on a web application, you probably have a custom 503 site, showing your customers that the servers are currently lying on the operating table.

At the dynamic ridesharing service flinc, we touch a certian file on our reverse proxies (e.g. using capistrano deploy:web:disable) when maintenance begins. Nginx then serves a static “we’ve disabled the site for maintenance” site, instead of the actual content.

But wouldn’t it be nice to test your web application before going live for your customers? It sure would. Unfortunately, this is not as simple as a task as you might think, because you cannot nest if directives in an Nginx location and if is evil.

iptables-ng cookbook for chef

Today, I released iptables-ng, a cookbook to maintain iptables rules on different machines using chef.

But why another cookbook? There are two fairly often used around

Well, I wanted a tool which can do all the following:

  • Configure iptables rules in a consistent and nice way for all distributions
  • Be configured by using LWRPs only
  • Be configured by using node attributes only
  • Respect the way the currently used distribution stores their rules
  • Provide a good-to-read and good-to-maintain way of deploying complex iptables rulesets
  • Provide a way of specifying the order of the iptables rules, in case needed
  • Only run iptables-restore once during a chef run, and only if something was actually changed
  • Support both, ipv6 as well as ipv4
  • Be able to assemble iptables rules from different recipes (and even cookbooks), so you can set your iptables rule where you actually configure the service

ipswitch - migrate IP addresses without downtime

When doing quick maintenance tasks on a server, you can use the following approach to keep your site available:

  • Failover the backnet IP address of the host to another host
  • Use arping to tell the network that this IP was switched
  • Remove the IP from the host that needs maintenance

In case you do not have a full high-availability setup available, you can use ipswitch, a small tool I wrote to assist with this kind of simple failover tasks.

You can install it using

$ gem install ipswitch

apt-get cleanup commands

Just a short post about some useful cleanup commands for Debian and Ubuntu systems. There are (to my knowledge) no build in task solving the following things

  • Remove old kernels (while keeping the currently running and the latest)
  • Purge removed packages (especially after autoremoving unneeded dependencies)

Howto use chef with ssl

By default, the connections between the chef-client and the chef-server are not secured. This is a short post on howto encrypt and verify your connections.

As of chef-11 (unlike chef-10), SSL is enabled by default. But (naturally, as Opscode cannot create trusted certificates for your domain) the certificates are not verified. This essentially means that the connection is not secure at all.

Unless you only use chef in a trusted network, you should invest some time in securing your clients connections.

Chef deploy_revision and Capistrano git_style

One thing that was annoying me for a long time, was that, using Capistrano deployment, you cannot spawn a new vanilla virtual machine, and bring it to a fully up-and-running state with just one Chef command.

make deploy_revision compatible with Capistrano, so deployments can happen with Capistrano, until we’ve decided to fully migrate to Chef, or to stick with the push deployment