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Make Ansible "postgresql_ping" fail if the database does not exist

Ansible has a very useful module "postgresql_ping" which checks connectivity to the database server. I'm using it in quite a few Playbooks as first step just to ensure that the database server is present - this fails early if there is a problem which otherwise just prevents the rest of the Playbook to work properly.

TASK [Check if database is available]
[WARNING]: PostgreSQL server is unavailable: could not connect to server: No such file or directory         Is the server running locally and accepting         connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
fatal: [127.0.0.1]: FAILED! => {"changed": false, "failed_when_result": true, "is_available": false, "server_version": {}}

 

However this module does not check if the database exists, just if the server is reachable. Example Playbook:

- name: Check if database is available
  postgresql_ping:
    db: "testdb"
  become: yes
  become_user: postgres

When I run the Playbook:

TASK [Check if database is available]
[WARNING]: PostgreSQL server is unavailable: FATAL:  database "testdb" does not exist
ok: [127.0.0.1]

 

As you can see, the database "testdb" does not exist. Which for the module is a reason to raise a warning, but not  a reason to fail.

One possible solution is to let this module do it's work, and add a "postgresql_db" call next, which ensures that the database is created. But not every Playbook is supposed to create and populate a database, and has all the required parameters (owner, encoding, template ect) available. Therefore it would be nice if "postgresql_ping" fails early if the database in question doesn't exist. That's possible, with two more lines of code:

- name: Check if database is available
  postgresql_ping:
    db: "testdb"
  become: yes
  become_user: postgres
  register: ping_database
  failed_when: ping_database.warnings is defined

And the Playbook run:

TASK [Check if database is available]
[WARNING]: PostgreSQL server is unavailable: FATAL:  database "testdb" does not exist
fatal: [127.0.0.1]: FAILED! => {"changed": false, "failed_when_result": true, "is_available": false, "server_version": {}}

Together with "any_errors_fatal: True" this ends the entire Playbook early enough before I have to debug the problem later on.

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Online indicator for remote controllable power plugs in openHAB

Recently I installed a number of new power sockets (like this one). The Hue bridge can not only add each switch to a light group, but also reports each plug as a Thing in openHAB. There I thought it will be a nice touch if openHAB actually reports when it sees a device plugged in. The power socket has a LED which turns on when the plug is on. The Hue bridge reports OFFLINE and ONLINE. That's useful.

The plan is to turn the LED light - and the power plug - on and off for a few second.

 

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Restic backup

Was asked quite a few times how I do my backups with Restic.

For more than 10 years I was using "Duplicity" for backups, but in 2019 I changed to Restic. The main reason for the change was that Duplicity still can't handle "Big Data", as in: larger directories. In 2009 someone opened an issue on the Duplicity bugtracker, and this problem still exists as of today. For about two years I was shifting around the problem, excluding files, trying to make the sigfile smaller. But at some point I decided that it is enough and I need to change the tool.

Duplicity knows two backup modes: "full backup" and "incremental backup". Once in a while you take a full backup, and then you add incremental backups to that full backup. In order to restore a certain backup you need the full backup and the incremental backups. Therefore my go-to mode was to always have two full backups and a couple incremental backups in-between. Even if something goes wrong with the latest full backup, I can still go back to the previous full backup (of course with some changes lost, but that's still better than nothing). When taking a new full backup, the oldest one is only deleted when the new one is completed. Accordingly when a new incremental backup is created, it's a new set of files. Removing the backup removes all the files from this incremental backup. That worked well, but needed scheduling. Over time I wrote a wrapper script around Duplicity, which did schedule new full and incremental backups.

Restic works in a different way. There is no concept of "full backup" and "incremental backup". Basically every backup is a full backup, and Restic figures out which files changed, got deleted, or added. Also it does deduplication: if files are moved around, or appear multiple times, they are not added multiple times into the backup. Deduplication is something which Duplicity can't do. But because Restic can do deduplication, there is no common set of files which belong to a single snapshot. Data blobs from one backup can stay in the repository forever, removing snapshots might not remove any files at all.

Restic on the other hand needs "prune" to remove old data. A snapshot can be removed according to the policy specified, but this does not remove the data from the backup directory. A "prune" run will go over the data and remove any block which is no longer needed.

My first question - after figuring out which other backup tool to use: shall I replicate the wrapper script, or try something else? Given that the backup doesn't need complex scheduling, I decided against writing a complex wrapper. And since I am now deploying all devices with Ansible, I decided to integrate this into my Playbooks, and deploy a set of shell scripts. The goal was to have a small number of dedicated scripts doing the daily backup work, and another set of "helper" scripts which I can use to inspect the backup, modify it, or restore something.

My main goals for this: "small number of programs/scripts" (Unix style: each tool does one job), "rapid development" (don't spend weeks writing another scheduler), "rapid deployment" (re-run Playbooks and let Ansible deploy this to all devices).

 

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Add a Google Calendar to openHAB

openHAB can integrate Google Calendars. The functionality is kind of limited, it can only see the current and the next calendar event, but in my case that is enough. More about the use case in another blog post.

There are three different calendar bindings available, let's have a quick look:

  • CalDAV Personal Binding: this is a v1 binding, which means it will no longer work in the soon-to-be-released openHAB v3. Apparently this works with Google calendars, but has performance issues. It can show the current and next event.
  • Google Calendar Scheduler: also a v1 binding. Needs more work for presense simulation, and additional bindings.
  • iCalendar Binding: v2 binding, should work with v3. It can show the current and next event. That's the one I'm going to use.

 

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openHAB: faster loading of rules files

openHAB rules files are lazy loaded. When a rule is used the first time, the entire rule file is loaded and compiled, which apparently is single-threaded and takes a couple seconds. Even on a reasonable powerful Rasperry Pi 4. This happens both after restarting openHAB and after changing the rules file. It also means that whatever the rule in question is supposed to do has to wait a couple seconds when requested for the first time. Imagine you have a light switch, enter a room, press the switch, and it takes 5-10 seconds until the light comes on.

To work around this problem, I add a piece of code in all rules files which triggers an immediate action right after loading the file. This way the rules file is already pre-loaded (which again takes a couple seconds, but likely at a time when the rule is not needed right now).

 

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Audio reminders in openHAB

A while ago someone mentioned "reminders" used in their home audio system, and I took that idea and implemented something similar in openHAB.

The basic idea is that I can send scheduled notifications to any audio sink openHAB is using, possibly more than one audio sink for one message. Also I want to differentiate between a simple audio sound, and text output.

For the text audio output I installed Text-to-Speech a while ago, this enables the ability to output text as audio in different languages. In addition I want an information when a reminder is "fired" in my Telegram control channel. As audio sink I'm mostly using ChromeCasts here, but anything openHAB can connect to is usable here.

 

 

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openHAB, Telegram Bot and quoting URLs

A while ago I integrated DWD warnings (Deutscher Wetterdienst) into our home automation system, and receive severe weather notifications ever since then. That works quite good, but it was missing a weblink with more details - or if you want to forward the warning to someone it would be useful to have a link to the warning as well. The DWD binding does not provide that piece of information, but it is easy enough to add - or so I thought.

 

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Text-to-Speech in openHAB

In my ongoing endeavor to improve our home, a while ago I added a notification when the washing machine and the dryer are finished. The notification is send to a Telegram channel. Over the summer vacation I added a number new ChromeCast Audio devices (Google no longer offers the Audio CC, if you need one get one now). One is placed in the kitchen. Not only can I listen to music while eating breakfast, I can also output notifications, by using the CC as an audio sink in openHAB.

To make that useful, I decided to use a Text-to-Speech system. openHAB offers a couple different TTS systems, however most of them need a cloud integration, and therefore a working Internet connection. The "Pico TTS" works standalone, and was my favorite choice for this implementation.

 

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openHAB and Tankerkönig gas prices + Telegram integration - Second iteration

In my previous blog post about "Tankerkönig" I explained the details of how to integrate this binding into openHAB and provide a Telegram interface.

Someone on the openHAB community forum pointed out that Telegram bots allow queries, where one can present the user with options, and the user only has to click on one of the options. That makes it easier to use, and less typing is required as well. I went ahead and implemented that.

 

 

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Use namespace as global variable in Ansible Jinja templates

A simple task, or so I thought: in a Jinja template keep track of the number of items in a loop. And then use that count afterwards.

Disclaimer: the number of items is not equal the number of times the loop runs, so I can't use the loop variables.

Turns out that Jinja has other opinions, and variables inside a loop are all local. When a variable is changed inside the loop, the scoop of the variable stays local, and once the loop ends the original value of the variable is restored. That's even true for variables which are created outside the loop.

 

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