Multi target support

[adnull]

This is multi-target support implementation of the mongodb_exporter. This version can be used with prometheus to allow scraping multiple hosts metrics by running just single instance of the exporter.

The code contains minimal changes to implement this feature and doesn't conflict with the main branch.
Multiple targets can be specified in the mongodb.uri option as comma separated list of server URIs
Also, a new option was added - mongodb.connect-timeout-ms which sets default server connection timeout.
Usage notes are located in the readme file in my fork https://github.com/adnull/mongodb_exporter_mt

---

• Tests passed.
• Fix conflicts with target branch.

[adnull]

@JiriCtvrtka Hi! Seems like there are problems with the test-cluster. I've checked all tests on my local machine and they are failing like this only if test-cluster didn't set up properly.
For example, this error:

    testutils.go:135:
        	Error Trace:	/Users/user/projects/mongodb_exporter/internal/tu/testutils.go:135
        	Error:      	Received unexpected error:
        	            	server selection error: context deadline exceeded, current topology: { Type: Single, Servers: [{ Addr: 127.0.0.1:17001, Type: Unknown, Last error: dial tcp 127.0.0.1:17001: connect: connection refused }, ] }

means that node mongo-1-1 is down.
Probably it is not enough disk space to run cluster. Or it needs a little bit more time to come up before running tests.

[JiriCtvrtka]

@adnull Hi. Yes I am on it. I also noticed some minor problems in exporter (not in your PR). I will merge this once since it will be fixed. Thank you for your PR and efford.

[BupycHuk]

A few minor comments.
Once PR with test fixes is merged we will check that tests are not failed and merge this PR. As far as I see there are no backward incompatible changes.

[BupycHuk]

@adnull please fix the linter
@JiriCtvrtka PTAL

[adnull]

@adnull please fix the linter

Sure, forgot to format. done.

[BupycHuk]

@adnull, linters are still complaining. Please address them.

[adnull]

@adnull, linters are still complaining. Please address them.

Sure, i am looking into it and can't get why they fail with the errors like tagalign and nlreturn on the code which is no different from the main code while the same actions in my own repository finish successfully.

[BupycHuk]

@adnull Seems like your changes wasn't related to linter complains. They existed before, but because you changed those lines linter started complaining. So I merged as is.

[adnull]

Oh, they almost broke my mind :) Seems like linters list should be adjusted...

[Swoods3]

Splitting mongodb_uri with commas and within a double quote for example: "mongodb:connection_string" is no longer acceptable. Is there a way to make the config file backwards compatible as it is for versions 0.0.4 to 3.0.1?

Current target is a single cluster multi port as defined by Atlas to monitor and has been working for the last year ENCLOSED in double quotes and has comma separated the 3 target cluster ports as the teams use to connect to the atlas and has been working, but no longer works with version 3.1.0. Here is an example that used to work:

mongodb_uri: "mongodb://user:[email protected]:20000,nameN.mongodb.net:20001,nameN.mongodb.net:20002/dbname-qa?authSource=admin&replicaSet=name&ssl=true&retryWrites=true&w=majority"

[adnull]

Splitting mongodb_uri with commas and within a double quote for example: "mongodb:connection_string" is no longer acceptable. Is there a way to make the config file backwards compatible as it is for versions 0.0.4 to 3.0.1?

I've got the idea and will take a look shortly

[Swoods3]

Thanks so much!

…

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[adnull]

@Swoods3 i've created a pull-request (#780) regarding the problem you've described. But while it is being waited to be approved and included to a release you can use manually compiled code from the branch or try using my docker image with this feature included: https://hub.docker.com/r/adnull/mongodb_exporter

[Swoods3]

@adnull Thanks so much!