Logging Guidelines

https://blueprints.launchpad.net/nova/+spec/log-guidelines

Problem description

The current state of logging both within and between OpenStack components is inconsistent to the point of being somewhat harmful by obscuring the current state, function, and real cause of errors in an OpenStack cloud. A consistent, unified logging format will better enable cloud administrators to monitor and maintain their environments.

Before we can address this in OpenStack, we first need to come up with a set of guidelines that we can get broad agreement on. This is expected to happen in waves, and this is the first iteration to gather agreement on.

Proposed change

Definition of Log Levels

http://stackoverflow.com/a/2031209 This is a nice writeup about when to use each log level. Here is a brief description:

  • Debug: Shows everything and is likely not suitable for normal production operation due to the sheer size of logs generated
  • Info: Usually indicates successful service start/stop, versions and such non-error related data. This should include largely positive units of work that are accomplished (such as starting a compute, creating a user, deleting a volume, etc.)
  • Audit: REMOVE - (all previous Audit messages should be put as INFO)
  • Warning: Indicates that there might be a systemic issue; potential predictive failure notice
  • Error: An error has occurred and an administrator should research the event
  • Critical: An error has occurred and the system might be unstable; immediately get administrator assistance

We can think of this from an operator perspective the following ways (Note: we are not specifying operator policy here, just trying to set tone for developers that aren’t familiar with how these messages will be interpreted):

  • Critical : ZOMG! Cluster on FIRE! Call all pagers, wake up everyone. This is an unrecoverable error with a service that has or probably will lead to service death or massive degredation.
  • Error: Serious issue with cloud, administrator should be notified immediately via email/pager. On call people expected to respond.
  • Warning: Something is not right, should get looked into during the next work week. Administrators should be working through eliminating warnings as part of normal work.
  • Info: normal status messages showing measureable units of positive work passing through under normal functioning of the system. Should not be so verbose as to overwhelm real signal with noise. Should not be continuous “I’m alive!” messages.
  • Debug: developer logging level, only enable if you are interested in reading through a ton of additional information about what is going on.
  • Trace: In functions which support this level, details every parameter and operation to help diagnose subtle bugs. This should only be enabled for specific areas of interest or the log volume will be overwhelming. Some system performance degradation should be expected.

Proposed Changes From Status Quo

  • Deprecate and remove AUDIT level

Rationale, AUDIT is confusing, and people use it for entirely the wrong purposes. The origin of AUDIT was a NASA specific requirement which is not longer really relevant to the current code.

Information that was previously being emitted at AUDIT should instead be sent as notifications to a notification queue. Note: Notification formats and frequency are beyond the scope of this spec.

  • Define TRACE logging level

TRACE is a logging keyword that is understood by most logging tools. OpenStack has repurposed this in the past to not be TRACE logging but instead be used whenever a Stacktrace was dumped.

Stack traces should be logged at ERROR level (they currently aren’t).

TRACE should be defined as log level 5 in python (which is lower than DEBUG), and LOG.trace support should be added to oslo logger. LOG.trace can then be used for deep tracing of code.

Overall Logging Rules

The following principles should apply to all messages

Log messages at Info and above should be a “unit of work”

The Info log level is defined as: “normal status messages showing measureable units of positive work passing through under normal functioning of the system.”

A measurable unit of work should be describable by a short sentence fragment, in the past tense with a noun and a verb of something significant.

Examples:

Instance spawned

Instance destroyed

Volume attached

Image failed to copy

Words like “started”, “finished”, or any verb ending in “ing” are flags for non unit of work messages.

Debugging start / end messages

At the Debug log level it is often extremely important to flag the beginning and ending of actions to track the progression of flows (which might error out before the unit of work is completed).

This should be made clear by there being a “starting” message with some indication of completion for that starting point.

In a real OpenStack environment lots of things are happening in parallel. There are multiple workers per services, multiple instances of services in the cloud.

Examples of Good and Bad uses of Info

Below are some examples of good and bad users of info. In the Good examples we can see the ‘noun / verb’ fragment for a unit of work (successfully is probably superfluous and could be removed).

In the bad examples we see trace level thinking put into INFO and above messages.

Good

2014-01-26 15:36:10.597 28297 INFO nova.virt.libvirt.driver [-]
[instance: b1b8e5c7-12f0-4092-84f6-297fe7642070] Instance spawned
successfully.

2014-01-26 15:36:14.307 28297 INFO nova.virt.libvirt.driver [-]
[instance: b1b8e5c7-12f0-4092-84f6-297fe7642070] Instance destroyed
successfully.

Bad

2014-01-26 15:36:11.198 INFO nova.virt.libvirt.driver
[req-ded67509-1e5d-4fb2-a0e2-92932bba9271
FixedIPsNegativeTestXml-1426989627 FixedIPsNegativeTestXml-38506689]
[instance: fd027464-6e15-4f5d-8b1f-c389bdb8772a] Creating image

2014-01-26 15:36:11.525 INFO nova.virt.libvirt.driver
[req-ded67509-1e5d-4fb2-a0e2-92932bba9271
FixedIPsNegativeTestXml-1426989627 FixedIPsNegativeTestXml-38506689]
[instance: fd027464-6e15-4f5d-8b1f-c389bdb8772a] Using config drive

2014-01-26 15:36:12.326 AUDIT nova.compute.manager
[req-714315e2-6318-4005-8f8f-05d7796ff45d FixedIPsTestXml-911165017
FixedIPsTestXml-1315774890] [instance:
b1b8e5c7-12f0-4092-84f6-297fe7642070] Terminating instance

2014-01-26 15:36:12.570 INFO nova.virt.libvirt.driver
[req-ded67509-1e5d-4fb2-a0e2-92932bba9271
FixedIPsNegativeTestXml-1426989627 FixedIPsNegativeTestXml-38506689]
[instance: fd027464-6e15-4f5d-8b1f-c389bdb8772a] Creating config
drive at
/opt/stack/data/nova/instances/fd027464-6e15-4f5d-8b1f
-c389bdb8772a/disk.config

This is mostly an overshare issue. At Info these are stages that don’t really need to be fully communicated.

Messages shouldn’t need a secret decoder ring

Bad

2014-01-26 15:36:14.256 28297 INFO nova.compute.manager [-]
Lifecycle event 1 on VM b1b8e5c7-12f0-4092-84f6-297fe7642070

General rule, when using constants or enums ensure they are translated back to user strings prior to being sent to the user.

Specific Event Types

In addition to the above guidelines very specific additional requirements exist.

WSGI requests

Should be:

  • Logged at INFO level
  • Logged exactly once per request
  • Include enough information to know what the request was

The last point is notable, because some POST API requests don’t include enough information in the URL alone to determine what the API did. For instance, Nova Server Actions (where POST includes a method name).

Rationale: Operators should be able to easily see what API requests their users are making in their cloud to understand the usage patterns of their users with their cloud.

Operator Deprecation Warnings

Should be:

  • Logged at WARN level
  • Logged exactly once per service start (not on every request through code)
  • Include directions on what to do to migrate from the deprecated state

Rationale: Operators need to know that some aspect of their cloud configuration is now deprecated, and will require changes in the future. And they need enough of a bread crumb trail to figure out how to do that.

REST API Deprecation Warnings

Should be:

  • Not logged any higher than DEBUG (these are not operator facing messages)
  • Logged no more than once per REST API usage / tenant. Definitely not on every REST API call.

Rationale: The users of the REST API don’t have access to the system logs. Therefore logging at a WARNING level is telling the wrong people about the fact that they are using a deprecated API.

Deprecation of User facing API should be communicated via User facing mechanisms, being API change notes associated with new API versions.

Stacktraces in Logs

Should be:

  • exceptional events, for unforeseeable circumstance that is not yet recoverable by the system.
  • Logged at ERROR level
  • Considered high priority bugs to be addressed by the development team.

Rationale: The current behavior of OpenStack is extremely stack trace happy. Many existing stack traces in the logs are considered normal. This dramatically increases the time to find the root cause of real issues in OpenStack.

Logging by non-OpenStack Components

OpenStack uses a ton of libraries, which have their own definitions of logging. This causes a lot of extraneous information in normal logs by wildly different definitions of those libraries.

As such, all 3rd party libraries should have their logging levels adjusted so only real errors are logged.

Currently proposed settings for 3rd party libraries:

  • amqp=WARN
  • boto=WARN
  • qpid=WARN
  • sqlalchemy=WARN
  • suds=INFO
  • iso8601=WARN
  • requests.packages.urllib3.connectionpool=WARN
  • urllib3.connectionpool=WARN

Alternatives

Continue to have terribly confusing logs

Data model impact

NA

REST API impact

NA

Security impact

NA

Notifications impact

NA

Other end user impact

NA

Performance Impact

NA

Other deployer impact

Should provide a much more standard way to determine what’s going on in the system.

Developer impact

Developers will need to be cognizant of these guidelines in creating new code or reviewing code.

Implementation

Assignee(s)

Assignee is for moving these guidelines through the review process to something that we all agree on. The expectation is that these become review criteria that we can reference and are implemented by a large number of people. Once approved, will also drive collecting volunteers to help fix in multiple projects.

Primary assignee:
Sean Dague <sean@dague.net>

Work Items

Using this section to highlight things we need to decide that aren’t settled as of yet.

Proposed changes with general consensus

  • Drop AUDIT log level, move all AUDIT message to either an INFO log message or a notification.
  • Begin adjusting log levels within projects to match the severity guidelines.

Dependencies

NA

Documentation Impact

Once agreed upon this should form a more permanent document on logging specifications.

References