lineinfile Best Practice?

[Josef Fortier]

What ideas do others have on Best Practice for using lineinfile?

As a potential conversation starter, here's a couple of ideas that have recently gelled for me:

1) Use two rules:

* First delete all versions of the line

* Then add the finished version of the line.

This makes the process more idempotent (which, granted lineinfile has inherent problems with....)
For context, this idea gells around adding a mailrelay statement for postfix's main.cf. In my environment I have 4 different platforms with various ad-hoc maintenance (covering quite a few years).

2) Use a (trailing) comment header (i.e. a "here are our changes" line) and then append changes after this.

Some more context here, I suspect lineinfile appeals to those of us who have an existing set of servers that we are incrementally bringing into line. The "correct" path is likely to use a template of a file, but that requires determining which of the (our various) distro's is the "correct" set of settings. For something like "use our mail relay" this is a fairly large hurdle.

Thanks for any comments in advance :-)

[Brian Coca]

rule 0) If at all possible, use template module instead, it gives you
full control and verification.



--
Brian Coca

[Josef Fortier]

Your reply, while correct, seems designed to shut down useful feedback. Perhaps you did not mean it that way.

I noted up front that:

>  The "correct" path is likely to use a template of a file

I'm aware that lineinfile has problems. Which is why I'm requesting feedback on how one might use it best.

For a lot of use cases lineinfile, is an immediately useful expedient step, with advantages that far outweigh it's disadvantages.
In the case I suggested, for example:

> adding a mailrelay statement for postfix's main.cf.

I have 6 different legacy versions of main.cf floating around, covering two different distributions. Doing it the correct way means:

1) Reading through each version to determine if there is something special about a given setup.

2) Researching the parts I do not fully understand

3) Determining which of the differing parts should be in the final version

That work is good work, but it's a lot of work. It's not unrealistic to suggest that's a week or more of work (postfix is pretty flexible, which translates to reading though a *lot* of options).

Most of those options don't really have a final "correct" setting. But I know up front what relayhost should be.

[esco real]

Hello Josef,

could you explain what exactly the problem is here? Maybe posting some examples with actual/ and expected results?

I have different relay hosts in main.cf, too. I just use a var per group and lineinfile to set relay and didn't have a problem with that.

esco

[Josef Fortier]

Hi Esco:

On Tuesday, October 20, 2015 at 3:31:11 PM UTC-5, esco real wrote:
could you explain what exactly the problem is here? Maybe posting some examples with actual/ and expected results?

Nothing insurmountable. Just trying to formulate in my own mind what works the best. I was/am able to work around the issues I'll detail, but I'd rather have had a uniform approach up front.

First Issue: pre-existing relayhost on a handful of servers.
I used regex: to catch the empty hosts
Unintended result, hosts with existing relayhost had two set.

Second issue: Too loose/tight regex (either or both).
Correcting the first issue either led to duplication's or just updated the duplicates to uniform values.

It looks like backrefs is a partial fix for this, but after a little reflection I realized that in this case (and many other cases like it) my best approach is to create two rules, one that deletes the line first, and then a role to add it. In particular this catches multiple lines in file. It's also easier to get the regex correct (i.e, "delete all other lines that might set the var")

[Javier Palacios]

Hello Josef,

you might have a look to the augeas role. I've not used it with ansible but with puppet, and if you are changing a standard configuration file is probably the best approach. Even if you don't want to use the role, use augeas with a 'command' might also help

Javier Palacios

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