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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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openHAB: stop a ChromeCast

There are a number of ChromeCasts in our setup. I'm adding (physical) switches to turn displays on and off, and primarily control the volume. When I turn the display off, I also want the ChromeCast to stop doing whatever it is doing right now (stop streaming), and go back to the default application (for video CC).

The openHAB ChromeCast binding has a separate channel for that:

Switch    chromecast_chromecast_dfb5af5187ce1135b276239130aef282_stop     { channel="chromecast:chromecast:dfb5af5187ce1135b276239130aef282:stop" }

However since the channel is named "stop", it has to be "enabled" with "ON". Doesn't make sense? It is as it is:

chromecast_chromecast_dfb5af5187ce1135b276239130aef282_stop.sendCommand(ON)

And the result:

2021-01-18 17:13:20.305 [ome.event.ItemCommandEvent] - Item 'chromecast_chromecast_dfb5af5187ce1135b276239130aef282_stop' received command ON
2021-01-18 17:13:20.321 [nt.ItemStatePredictedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_stop predicted to become ON
2021-01-18 17:13:20.443 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_appName changed from <...> to UNDEF
2021-01-18 17:13:20.451 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_appId changed from <...> to UNDEF
2021-01-18 17:13:20.455 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_statustext changed from Casting: <...> to UNDEF
2021-01-18 17:13:20.457 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_idling changed from OFF to ON
2021-01-18 17:13:23.888 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_appName changed from UNDEF to Backdrop
2021-01-18 17:13:23.893 [vent.ItemStateChangedEvent] - chromecast_chromecast_dfb5af5187ce1135b276239130aef282_appId changed from UNDEF to E8C28D3C

 

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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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openHAB: Configuration model '....rules' has errors, therefore ignoring it: no viable alternative at input '...'

The openHAB rule system is not very helpful by pointing out when it's missing something, or when there is an error to actually point to the problem.

Was debugging an error message for a while and couldn't figure out what is wrong:

Configuration model '....rules' has errors, therefore ignoring it: [152,5]: no viable alternative at input '...'

The line number specified was somewhere else in the file, and had nothing to do with the rule in question. After removing almost everything from the rule, except a logInfo() message, the error still happened - and then it occured to me: I forgot to specify "Item".

My faulty code was:

rule "Rule Name"
when
    Sensor_name received update
then

where it should have been:

rule "Rule Name"
when
    Item Sensor_name received update
then

Error message totally not helpful ...

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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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Improve openHAB Rules response time

By default, openHAB only starts 5 threads to deal with execution of Rules. That's not a lot, and if all threads are busy, rules have to wait until a slot is free. This results in slow Rule response time.

This can be improved.

 

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openHAB: Turn display on and off for a Video ChromeCast

After figuring out if a ChromeCast is currently used, it was time to fix a long-standing problem. At home we don't have TVs, just "dumb" displays, and stream content using ChromeCasts. However a video ChromeCast never really turns off, but keeps the display running, using a "Backdrop" app. This app keeps showing pictures on the display when the ChromeCast is not used otherwise, effectively preventing any powersafe mode.

That's both annoying (who wants to have pictures shown in the living room or working room all night), and consumes energy. It's also intentional by Google. So far we had to turn the display on and off manually, which is inconvenient.

 

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openHAB: detect if a ChromeCast is currently used or idle

We have a couple of Audio and Video ChromeCasts in use. For an upcoming project I need to figure out if any of them is currently used. That is different for the Audio and the Video devices: the Audio just goes idle=ON, the Video devices however load the "Backdrop" app and show pictures when idling. Google for whatever reason does not want the attached monitor to go in powersafe mode. So much for saving energy ...

All of the action needs between a few milliseconds and 2-3 seconds once you start/stop using the ChromeCast.

A previous blog post explains how I add the ChromeCast devices. And I have monitoring in place.

 

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