Eliminate logspam using filelog monitor

[skaven81]

When using a filelog monitor, the top-level pluginConfig.message filter provides a limited stream of log events to be checked against the rules[].pattern. I thus expect it to be normal for most log events to fail to match the top-level pluginConfig.message filter. Such a condition should not trigger a warning-level log message. And in fact such log messages should be suppressed by default, unless -v=5 or higher is used for troubleshooting/debug purposes.

See also #1038

As discussed in the comments below, the original intent was that the pluginConfig.message configuration setting for logMonitors was expected to match all of the "expected" log events in the log file, and that the subsequent rules[].pattern regexes then differentiate between different types of failure modes in the log stream. Thus, the warning message that I've proposed changing to "info" level and suppressing in normal operation, was expected to only appear in cases where unexpected log events show up in the log stream.

But this causes problems when trying to detect node problems in a log file that has a wide array of event messages. Because the last pluginConfig.message regex capture group is what is used in node condition and Event message fields, it is only possible to include details about a single failure mode in a given logMonitor configuration. When viewed through this lens, the logMonitor architecture actually works quite well:

• Each logMonitor JSON file represents a single node failure mode
• Each logMonitor JSON file has its pluginConfig.message regex configured to isolate the class of log messages in the log file that are related to the failure mode, then use the last capture group to extract a diagnostic message to be included with the status condition or Event
• The rules list in the logMonitor JSON enumerate the various sub-classes of the failure mode, with some perhaps generating permanent node conditions, while others generate temporary Events.

The problem with using logMonitors in this way, is that using pluginConfig.message to filter out basically all of the log messages in the log file, means every log event generates a warning message due to pluginConfig.message regex not matching. This creates a massive amount of unnecessary logspam that can quickly fill up container log partitions and costs a fortune in enterprise log management platforms like Splunk and Datadog.

This PR makes the most direct and least-impact approach to resolving this problem, by simply making the Warning() level alert downgraded to Info() and preventing it from being emitted unless the NPD is executed with a non-default verbosity setting.

It is notable that this PR would not be required if a more comprehensive rework of the logMonitor message capture was performed. If the node condition and Event message was instead captured from the rules[].pattern regex instead of the pluginConfig.message regex, then logMonitors could remain configured with a broad capture mode that matches all or nearly all of the log messages in the file.

However, even with such a rework, I would still advise that the "log message doesn't match pluginConfig.message regex" alert message still be suppressed unless the administrator is explicitly debugging/troubleshooting NPD, as even in the case where the node condition/event message is captured from rules[].pattern (which would be my preference), I would still argue that many logMonitors would want to filter the log stream down to a known set of input strings that are then matched against the rule patterns. This allows the rule patterns to be simpler and easier to maintain, because they only have to match against a pre-filtered set of log events.

The specific use-case where this logspam problem originated is actually in one of the included sample log monitors: https://github.com/kubernetes/node-problem-detector/blob/master/config/disk-log-message-filelog.json - observe that pluginConfig.message only matches the log messages in /var/log/messages that actually match a failure condition. ALL other messages are filtered out (and thus trigger the warning log that I've modified in this PR).

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[hakman]

/ok-to-test

[hakman]

@wangzhen127 I am not sure if -v=5 the exact value, but I agree with the approach. Ref: https://github.com/kubernetes/node-problem-detector/issues/945 /lgtm

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[hakman]

/cc @wangzhen127 /assign @wangzhen127

[hakman]

CC @nikhil-bhat

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/remove-lifecycle stale

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