Adding a flag for splitting log output (--log-splitting)

[freddd]

Fixes #772

Basically, the issue is that logrus by default pipes all logs to stderr. This displays logs as being errors when they are actually level=info, etc in Google Stackdriver and DataDog.

Because of this, we are not able to have generic alerts on errors (as all lines are seen as errors). See screenshot in #772

The simplest way to test this PR is to run the application and redirect output:

The example below will send all logs to stderr (the default behavior).

external-dns --registry txt --txt-owner-id my-cluster-id --provider google --google-project example-project --source service --once --dry-run > 1.stdout 2> 2.stderr

This example shows the --log-splitting flag

external-dns --registry txt --txt-owner-id my-cluster-id --provider google --google-project example-project --source service --once --log-splitting --dry-run > 1.stdout 2> 2.stderr

To verify it, you can just cat 1.stdout and cat 2.stderr.

References:
sirupsen/logrus#403
Azure/open-service-broker-azure#25

[k8s-ci-robot]

Thanks for your pull request. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please follow instructions at https://git.k8s.io/community/CLA.md#the-contributor-license-agreement to sign the CLA.

It may take a couple minutes for the CLA signature to be fully registered; after that, please reply here with a new comment and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please sign in with your organization's credentials at https://identity.linuxfoundation.org/projects/cncf to be authorized.
• If you have done the above and are still having issues with the CLA being reported as unsigned, please email the CNCF helpdesk: helpdesk@rt.linuxfoundation.org

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
To fully approve this pull request, please assign additional approvers.
We suggest the following additional approver: hjacobs

If they are not already assigned, you can assign the PR to them by writing /assign @hjacobs in a comment when ready.

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[freddd]

/check-cla

[freddd]

/assign @hjacobs

[hjacobs]

this looks pretty hacky I must say

[freddd]

Yes, I agree. It is hacky. However I'm not really sure how to solve it in a nicer way as the only thing we can act on is the log line. Looking at the references it seems like they are not intending to fix it in logrus (especially not now since it is, according to the README, looking for a maintainer).

Any suggestions on how I could solve it in a nicer way? It's really annoying that all logs from external-dns shows up as errors, even if it's not.