Improve access logging

[mikz]

Use Cases

• Customize access log format per service (some custom format or JSON for example, liquid templating).
• Ability to disable access log conditionally per service. (Logging policy #856)
• Ship logs to syslog. ([cli] fix logging to syslog #858)
• Configure location of the access log file (for native deployments). (closes Make access_log location customizable #650)

Details

access_log directive offers if to enable/disable logging by setting a variable to 0/1 - this can be used to enable/disable logging by a policy.

It is possible the path parameter of the access_log directive can be a variable too and can be controlled from within a policy. Then we should consider using open_log_file_cache to files opened.

Syslog can be either achieved by setting syslog: path to the access_log directive, or we have to reuse https://github.com/nmasse-itix/apicast-logger to offer syslog from a policy.

Custom formats can be defined by log_format directive pointing just to a variable that is later populated by a policy.

[mikz]

Conclusion from my research:

1. syslog has to be set when the gateway starts and is global for all services. So it either logs to a file (stdout) or syslog.

2. Logging format can be customized, but it is pretty unpredictable because of nginx escaping the result. This can be turned off in nginx 1.13.10 but we have 1.13.6. We would have to wait for next OpenResty release to properly support this.

3. We can enable/disable logging per service easily.

[davidor]

So, regarding the format, we decided to wait for the next release of OpenResty (see @mikz comment above). Enabling/Disabling the service can be done with the policy introduced in #856 , and APIcast can be configured to log to syslog using an ENV.

I think there's nothing else we need to do for 2.3, so I'll remove this issue from the milestone.
/cc @andreumasferrer

[andreumasferrer]

ACK. Will update THREESCALE-1148 accordingly.

[metaversed]

hi @mikz Is it possible to expect this feature as a policy?

[davidor]

Done in #1089