JSON output format for the entrypoint script

[jayanthvn]

*Issue #907 , if available: JSON o/p format for the logs generated from entrypoint script

Description of changes:
dev-dsk-varavaj-2b-72f02457 % kubectl logs aws-node-2sq6w -n kube-system
{"level":"info","ts":"2020-07-01T02:21:56.104Z","caller":"entrypoint.sh","msg":"Copying CNI plugin binaries ... "}
{"level":"info","ts":"2020-07-01T02:21:56.120Z","caller":"entrypoint.sh","msg":"Starting IPAM daemon in the background ... "}
{"level":"info","ts":"2020-07-01T02:21:56.127Z","caller":"entrypoint.sh","msg":"Checking for IPAM connectivity ... "}
{"level":"info","ts":"2020-07-01T02:21:58.148Z","caller":"entrypoint.sh","msg":"Copying CNI plugin binary and config file ... "}
{"level":"info","ts":"2020-07-01T02:21:58.167Z","caller":"entrypoint.sh","msg":"Successfully copied CNI plugin binary and config file."}
{"level":"info","ts":"2020-07-01T02:21:58.168Z","caller":"entrypoint.sh","msg":"Foregrounding IPAM daemon ..."}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mogren]

I think I need to update #907 a bit. Having these log messages definitely helps us debug issues, so it would be better to have a function that logs messages in JSON format instead, so that it matches what zap outputs. Something like:

{"level":"info","ts":"2020-06-30T03:45:53.337Z","caller":"entrypoint.sh","msg":"Copying CNI plugin binary and config file ... "}
{"level":"info","ts":"2020-06-30T03:45:53.422Z","caller":"entrypoint.sh","msg":"Foregrounding IPAM daemon ... "}

[jayanthvn]

I think I need to update #907 a bit. Having these log messages definitely helps us debug issues, so it would be better to have a function that logs messages in JSON format instead, so that it matches what zap outputs. Something like:

{"level":"info","ts":"2020-06-30T03:45:53.337Z","caller":"entrypoint.sh","msg":"Copying CNI plugin binary and config file ... "}
{"level":"info","ts":"2020-06-30T03:45:53.422Z","caller":"entrypoint.sh","msg":"Foregrounding IPAM daemon ... "}

Thanks @mogren . It makes sense and I can look into it.

[nithu0115]

Thanks @jayanthvn for the fixing this. Need some more changes. Please see comments inline..

[nithu0115]

LGTM 👍

[mogren]

Thanks @jayanthvn and @nithu0115

[mogren]

Hadn't seen "${0##*/}" before 😄

[jayanthvn]

From stack overflow - "for the variable $0, and the pattern '/', the two hashes mean from the beginning of the parameter, delete the longest (or greedy) match—up to and including the pattern. So, where $0 is the name of a file, eg., $HOME/documents/doc.txt, then the parameter would be expanded as: doc.txt" :D