Add a function to get ip address for metrics crawler in k8s environment

[hitomitak]

This PR adds a function to get ip address in K8S environment for metrics crawler.
The detail information about metrics crawler is described at issue #196

IP address is not assigned to each docker and it is not included in docker inspect information (c.get_container_ip()) in k8s. So we pass IP address to the crawler by env variable (KUBE_POD_INFO) .

Signed-off-by: Hitomi Takahashi hitomi@jp.ibm.com

[codecov-io]

Codecov Report

Merging #335 into master will increase coverage by 0.21%.
The diff coverage is 98.01%.

@@            Coverage Diff             @@
##           master     #335      +/-   ##
==========================================
+ Coverage   88.48%   88.69%   +0.21%     
==========================================
  Files         117      117              
  Lines        4742     4867     +125     
==========================================
+ Hits         4196     4317     +121     
- Misses        546      550       +4

Impacted Files	Coverage Δ
...ns/applications/apache/apache_container_crawler.py	100% <100%> (ø)	⬆️
...ns/applications/tomcat/tomcat_container_crawler.py	100% <100%> (ø)	⬆️
...gins/applications/nginx/nginx_container_crawler.py	100% <100%> (ø)	⬆️
.../plugins/applications/db2/db2_container_crawler.py	100% <100%> (ø)	⬆️
.../applications/liberty/liberty_container_crawler.py	100% <100%> (ø)	⬆️
...gins/applications/redis/redis_container_crawler.py	92.72% <89.74%> (-7.28%)	⬇️

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[sahilsuneja1]

@tatsuhirochiba: Looks good. Can you please clarify the following:

1. 'IP address is not assigned to each docker container'- Why does this happen?
2. Is KUBE_POD_INFO a standard env var?
3. Would the alternative of getting ip addresses from inside the container work (as in os_container_crawler)?

[tatsuhirochiba]

For 1: At first, ip address is hidden from app container's docker inspect and some meaningful information are shown in pause container's docker inspect, so I was thinking about the following approaches.

a) preparing pod crawling mode (issued at #246)
b) preparing k8s client inside crawler
c) passing endpoint info via env and handling it within each container crawler plugin

option c) can minimize code change than option a) and b).

For 2: KUBE_POD_INFO is not standard env var. It is just defined for app metrics crawler plugins.

For 3: Thanks for nice info, I did not check some useful util code (os_utils.py and namespace.py). We can retrieve ip address with similar approach. I just confirmed that I can get ip with nsenter command in terminal.

We just try to use these utility code inside app metrics crawling plugin.

[sahilsuneja1]

Thanks for the clarifications @tatsuhirochiba!
Should we merge the current KUBE_POD_INFO version, or will you be creating an nsenter version? Your choice, really. We can even revisit Options 'a' and 'b' if you like.

[tatsuhirochiba]

@hitomitak will make nsenter version and then revise this PR, so we do not need to merge current KUBE_POD_INFO version, thanks!

[sahilsuneja1]

I'm sorry @hitomitak and @tatsuhirochiba. I just realized I did not tag the right person in my original comment and ended up following up with the wrong committer! :)

[hitomitak]

Thank you for the nice advice @sahilsuneja1
I modified the code to use run_as_another_namespace function.

[sahilsuneja1]

Thanks @hitomitak !