[Short Tip] Call Ansible or Ansible Playbooks without an inventory

Ansible is a great tool to automate almost anything in IT. However, one of the core concepts of Ansible is the inventory where the to be managed nodes are listed. However, in some situations setting up a dedicated inventory is overkill.

For example there are many situation where admins just want to ssh to a machine or two to figure something out. Ansible modules can often make such SSH calls in a much more efficient way, making them unnecessary – but creating a inventory first is a waste of time for such short tasks.

In such cases it is handy to call Ansible or Ansible playbooks without an inventory. In case of plain Ansible this can be done by  addressing all nodes while at the same time limiting them to an actual hostslist:

$ ansible all -i jenkins.qxyz.de, -m wait_for -a "host=jenkins.qxyz.de port=8080"
jenkins.qxyz.de | SUCCESS => {
    "changed": false, 
    "elapsed": 0, 
    "path": null, 
    "port": 8080, 
    "search_regex": null, 
    "state": "started"
}

The comma is needed since Ansible expects a list of hosts – and a list of one host still needs the comma.

For Ansible playbooks the syntax is slightly different:

$ ansible-playbook -i neon.qxyz.de, my_playbook.yml

Here the “all” is missing since the playbook already contains a hosts directive. But the comma still needs to be there to mark a list of hosts.

[Short Tip] Retrieve your public IP with Ansible

There are multiple situations where you need to know your public IP: be it that you set up your home IT server behind a NAT, be it that your legacy enterprise business solution does not work properly without this information because the original developers 20 years ago never expected to be behind a NAT.

Of course, Ansible can help here as well: there is a tiny, neat module called ipify_facts which does nothing else but retrieving your public IP:

$ ansible localhost -m ipify_facts
localhost | SUCCESS => {
    "ansible_facts": {
        "ipify_public_ip": "23.161.144.221"
    }, 
    "changed": false
}

The return value can be registered as a variable and reused in other tasks:

---
- name: get public IP
  hosts: all 

  tasks:
    - name: get public IP
      ipify_facts:
      register: public_ip
    - name: output
      debug: msg="{{ public_ip }}"

The module by default accesses https://api.ipify.org to get the IP address, but the api URL can be changed via parameter.

[Short Tip] Show all variables of a host

There are multiple sources where variables for Ansible can be defined. Most of them can be shown via the setup module, but there are more.

For example, if you use a dynamic inventory script to access a Satellite server many variables like the organization are provided via the inventory script – and these are not shown in setup usually.

To get all variables of a host use the following notation:

---
- name: dump all
  hosts: all

  tasks:
  - name: get variables
    debug: var=hostvars[inventory_hostname]

Use this during debug to find out if the variables you’ve set somewhere are actually accessible in your playbooks.

[Short Tip] Fix mount problems in RHV during GlusterFS mounts

When using Red Hat Virtualization or oVirt together with GLusterFS, there might be a strange error during the first creation of a storage domain:

Failed to add Storage Domain xyz.

One of the rather easy to fix reasons might be a permission problem: an initial Gluster exported file system belongs to the user root. However, the virtualization manager (ovirt-m bzw. RHV-M) does not have root rights and such needs another ownership.

In such cases, the fix is to mount the exported volume & set the user rights to the rhv-m user.

$ sudo mount -t glusterfs 192.168.122.241:my-vol /mnt
# cd /mnt/
# chown -R 36.36 .

Afterwarsd, the volume can be mounted properly. Some more general details can be found at RH KB 78503.

[Howto] Rebase feature branches in Git/Github

Updating a feature branch to the actual state of the upstream main branch can be troublesome. Here is a workflow that works – at least for me.

Developing with Git is amazing, due to the possibilities to work with feature branches, remote repositories and so on. However, at some point, after some hours of development, the base of a feature branch will be outdated and it makes sense to update it before a pull request is send upstream. This is best done via rebasing. Here is a short work flow for a typical feature branch rebase I often need when developing for example Ansible modules.

1. First, checkout the main branch, here devel.
2. Update the main branch from the upstream repository.
3. Rebase the local copy of the main branch.
4. Push it to the remote origin, most likely your personal fork of the Git repo.
5. Check out the feature branch
6. Rebase the feature branch to the main branch.
7. Force push the new history to the remote feature branch, most likely again your personal fork of the Git repo.

In terms of code this means:

$ git checkout devel
$ git fetch upstream devel
$ git rebase upstream/devel
$ git push
$ git checkout feature_branch
$ git rebase origin/devel
$ git push -f

This looks rather clean and easy – but I have to admit it took me quite some errors and Git cherry picking to finally get what is needed and what actually works.

[Short Tip] Workaround MIT-SHM error when starting QT/KDE apps with SUDO

Starting GUI programs as root usually is not a problem. In worst case, sudo inside a terminal should do the trick.

However, recently I had to start a QT application as sudo from within GNOME. It was the yubikey configuration GUI, a third party tool thus not part of any desktop environment. Executing the app failed, it only showed a gray window and multiple errors in the command line:

$ sudo /usr/bin/yubikey-personalization-gui 
X Error: BadAccess (attempt to access private resource denied) 10
  Extension:    130 (MIT-SHM)
  Minor opcode: 1 (X_ShmAttach)
  Resource id:  0x142
X Error: BadShmSeg (invalid shared segment parameter) 128
  Extension:    130 (MIT-SHM)
  Minor opcode: 5 (X_ShmCreatePixmap)
  Resource id:  0xfa
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
  Major opcode: 62 (X_CopyArea)
  Resource id:  0x2800015

Workarounds like pkexec and adding a policykit rule didn’t help, either. The error indicates that there is a problem with the MIT Shared Memory Extension of X.

A good workaround is to deactivate the usage of the extension on command line:

$ sudo QT_X11_NO_MITSHM=1 /usr/bin/yubikey-personalization-gui

It works like a charm.

[Short Tip] Git, cherry-pick and push

Much too often, when working with Git and working on long time pull requests, I tend to screw up the Git history. For that reason, I often have to cherry pick a commit into a new branch and push that one upstream to the feature branch – with force.

First, identify the actual commits you want to cherry pick. You need to get the correct hash there. Then, create a new branch, cherry pick the commit, force the new branch upstream, delete the old branch, and rename the new one.

git log --author liquidat
git branch mywork_feature_tmp
git cherry-pick abcdefgh123456
git push --force origin HEAD:mywork_feature
git checkout devel
git branch -D mywork_feature
git branch -m mywork_feature_tmp mywork_feature

My hope is that in some point in the future I will be able to fix such broken Git repos at that point without cherry-pick. But until then, the current way works for me…