SaltStack: edit yaml file on minion host based on salt pillar data - yaml

Question

Say the minion host has a default yaml configuration named myconf.yaml. What I want to do is to edit parts of those yaml entries using values from a pillar. I can't even begin to think how to do this on Salt. The only think I can think of is to run a custom python script on the host via cmd.run and feed it with input via arguments, but this seems overcomplicated.
I want to avoid file.managed. I cannot use a template, since the .yaml file is big, and can change by external means. I just want to edit a few parameters in it. I suppose a python script could do it but I thought salt could do it without writing s/w
I have found salt.states.file.serialize with the merge_if_exists option, I will try this and report.

Answer 1

You want file.serialize with the merge_if_exists option.
# states/my_app.sls
something_conf_file:
file.serialize:
- name: /etc/my_app.yaml
- dataset_pillar: my_app:mergeconf
- formatter: yaml
- merge_if_exists: true
# pillar/my_app.sls
my_app:
mergeconf:
options:
opt3: 100
opt4: 200
On the target, /etc/my_app.yaml might start out looking like this (before the state is applied):
# /etc/my_app.yaml
creds:
user: a
pass: b
options:
opt1: 1
opt2: 2
opt3: 3
opt4: 4
And would look like this after the state is applied:
creds:
user: a
pass: b
options:
opt1: 1
opt2: 2
opt3: 100
opt4: 200
As far as I can tell this uses the same algorithm as pillar merges, so e.g. you can merge or partially overwrite dictionaries, but not lists; lists can only be replaced whole.

Answer 2

This can be done for both json and yaml with file.serialize. Input can be inline on the state or come from a pillar. A short excerpt follows:
state:
cassandra_yaml:
file:
- serialize
# - dataset:
# concurrent_reads: 8
- dataset_pillar: cassandra_yaml
- name: /etc/cassandra/conf/cassandra.yaml
- formatter: yaml
- merge_if_exists: True
- require:
- pkg: cassandra-pkgs
pillar:
cassandra_yaml:
concurrent_reads: "8"