Archive for the 'Tools' Category

Ansible and Vagrant SSH Keys

I recently came across the question how to handle SSH keys with Vagrant and Ansible.

Vagrant

Traditionally all Vagrant boxes and VMs require a fixed login (vagrant) with a fixed SSH key. This was very convenient in a development context, but could raise security issues in case Vagrant VMs were used for anything important and users were not aware of the insecure key.

In current Vagrant versions only boxes (i. e. base images) use the insecure key. When Vagrant starts a new VM it generates a new individual SSH key for this instance. Vagrant keeps these custom keys in the .vagrant/machines subdirectory; so host to guest logins (like vagrant ssh) are still possible.

A vagrant up shows the multi-step procedure:

    workstation: Vagrant insecure key detected. Vagrant will automatically replace
    workstation: this with a newly generated keypair for better security.
    workstation: 
    workstation: Inserting generated public key within guest...
    workstation: Removing insecure key from the guest if it's present...
    workstation: Key inserted! Disconnecting and reconnecting using new SSH key...
==> workstation: Machine booted and ready!

To prevent this mechanism one can configure the VM with config.ssh.insert_key = False. This is necessary when modifying a box. Say you want to take a bento base box, install your development tools, and then repackage the VM as your own development box in order to distribute it to a development team. — With the default behaviour (config.ssh.insert_key = True) every repackage build would generate a new basebox with an individual ssh keypair; this makes the new boxes practically unusable, because every user would have to get and configure the custom SSH key for each box. With config.ssh.insert_key = False the box will retain the previous key; that means you users have the same experience as with a normal box.

Note: As a compromise between the two modes one can set a custom ssh key for all baseboxes with config.ssh.private_key_path. This might be useful for companies with many internal boxes. In this case one distribute one SSH key to use with all Vagrant boxes but not use the publicly known insecure standard key.

Ansible

If all VMs use the same SSH key the setup is straightforward: Configure all Vagrant VMs with config.ssh.insert_key = False or config.ssh.private_key_path and use that key for the Ansible login.

With Vagrant’s default behaviour there is no common SSH key for all VMs. In this case one has to configure Ansible to use the right keys for every VM, but the setup is still simple as long as you have the default /vagrant mount with the .vagrant subdirectory.

This subdirectory contains all Vagrant state and contains these files, right now the private_key is the important one:

$ find .vagrant/
.vagrant/
.vagrant/rgloader
.vagrant/rgloader/loader.rb
.vagrant/machines
.vagrant/machines/workstation
.vagrant/machines/workstation/virtualbox
.vagrant/machines/workstation/virtualbox/synced_folders
.vagrant/machines/workstation/virtualbox/vagrant_cwd
.vagrant/machines/workstation/virtualbox/index_uuid
.vagrant/machines/workstation/virtualbox/action_set_name
.vagrant/machines/workstation/virtualbox/private_key
.vagrant/machines/workstation/virtualbox/id
.vagrant/machines/workstation/virtualbox/box_meta
.vagrant/machines/workstation/virtualbox/action_provision
.vagrant/machines/workstation/virtualbox/creator_uid

I usually run one Vagrant VM as an Ansible controller (with node.vm.provision :ansible_local) and then 1 to N other VMs as installation targets. To enable access from the controller to the other VMs I include this line in the Ansible inventory: ansible_ssh_private_key_file=/vagrant/.vagrant/machines/{{ inventory_hostname }}/virtualbox/private_key

This should work just the same for running Ansible on your host machine and use it to provision the guest VMs. In this case the path would be a relative one: .vagrant/machines/....

The only important detail is the consistent naming of the VM in Vagrant and Ansible. With the ansible_ssh_private_key_file as above Vagrant’s VM name (set with config.vm.define) and Ansible’s inventory_hostname have to be the same. They are not required to match the guest’s hostname (config.vm.hostname), but I strongly recommend to either use the same value or use an obvious mapping. I usually try to use an FQDN for the hostname, and then use the short hostname (the first component) as the VM name and inventory name.

The only important detail is a consistent naming between Vagrant’s VM name (as set with config.vm.define), the VM’s hostname

Links 2017-05-15

On tools …

  • Setting the Record Straight: containers vs. Zones vs. Jails vs. VMs
    Solaris Zones, BSD Jails, and VMs are first class concepts. [..] Containers on the other hand are not real things.
  • CPU Utilization is Wrong
    The metric we all use for CPU utilization is deeply misleading, and getting worse every year. What is CPU utilization? How busy your processors are? No, that’s not what it measures. Yes, I’m talking about the “%CPU” metric used everywhere, by everyone.
  • Practical jq
    I really love jq, the JSON processor. It has changed my life and pretty much replaced Perl and Ruby as my ETL and data-munging go-to tools.
  • Reshaping JSON with jq
    Working with data from an art museum API and from the Twitter API, this lesson teaches how to use the command-line utility jq to filter and parse complex JSON files into flat CSV files.
  • A Visual Guide to What’s New in Swagger 3.0
    Over the past few years, Swagger 2 has become the de facto standard for defining or documenting your API. Since then, it’s been moved to the Linux foundation and renamed to OpenAPI Spec.
  • A plan for open source software maintainers
    As I envision it, a solution would look something like a cross between Patreon and Bugzilla: Users would be able sign up to “support” projects of their choosing […] and would be able to open issues.

let’s learn tcpdump

When I worked on IPv6 implementations I used tcpdump(1) on a daily basis. — Those times are long gone, but even today it is an extremely helpful tool. Just last week it helped me to debug a database connection problem.

To quote the great Rachel: “tcpdump -e can resolve a great many mysteries.”

If you never used tcpdump (or Wireshark) before then Julia Evan’s zine “let’s learn tcpdump” is a great place to start and to learn the 3-7 important command line parameters.

 

My First FreeBSD Port

A nice surprise last week: textproc/libcrm114 became my first official FreeBSD port.  :-)

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LaTeX minted

The minted package is a possible alternative to listing. It provides syntax highlighting for sourc code in LaTeX documents by calling the Python pygmentize tool.
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CUnit

As the name says CUnit is an xUnit implementation for the C programming language.

In comparison to dynamic programming languages the test organization requires much more manual glue code. Because C has no introspection one has to register every test case manually. Likewise there is no support for utilities like mock object generation or annotations.

On the other hand unit tests can be very useful in C, for example when implementing data structures. Test cases may isolate null pointer dereferencing and one can use valgrind on them to detect memory leaks at the lowest level.

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certutil

Ich möchte certutil für Unix haben… Dieses Windows-Tool dekodiert und verarbeitet ASN.1-Dateien für kryptographische Protokolle. Dabei kann es mehr als nur X.509-Zertifikate lesen (das geht auch mit den openssl-Tools gut) – ich brauchte es konkret um mir eine PKCS#7 Signatur anzeigen zu lassen.

(Ein Programm gleichen Namens ist übrigens Teil der Mozilla Network Security Services; aber auch das arbeitet „nur“ mit X.509 Zertifikaten.)