About This Document

THIS IS A DRAFT.

This document specifies logging conventions to be followed by ONAP component applications.  

ONAP logging is intended to support operability, debugging and reporting on ONAP. These guidelines address:

• Events that are written by ONAP components.
• Propagation of transaction and invocation information between components.
• MDCs, Markers and other information that should be attached to log messages.
• Human- and machine-readable output format(s).
• Files, locations and other conventions. 

Java is assumed, but conventions may also be implemented by non-Java components. 

Original 1.1 guidelines: https://wiki.onap.org/download/attachments/1015849/ONAP%20application%20logging%20guidelines.pdf?api=v2

Introduction

The purpose of ONAP logging is to capture information needed to operate, troubleshoot and report on the performance of the ONAP platform and its constituent components. Log records may be viewed and consumed directly by users and systems, indexed and loaded into a datastore, and used to compute metrics and generate reports. 

The processing of a single client request will often involve multiple ONAP components and/or subcomponents (interchangeably referred to as ‘application’ in this document). The ability to track flows across components is critical to understanding ONAP’s behavior and performance. ONAP logging uses a universally unique RequestID value in log records to track the processing of every client request through all the ONAP components involved in its processing.

A reference configuration of Elastic Stack can be deployed using ONAP Operations Manager. 

This document gives conventions you can follow to generate conformant, indexable logging output from your component.

How to Log

ONAP prescribes conventions. The use of certain APIs and providers is recommended, but they are not mandatory. Most components log via EELF or SLF4J to a provider like Logback or Log4j.

EELF

EELF is the Event and Error Logging Framework, described at https://github.com/att/EELF.

EELF abstracts your choice of logging provider, and decorates the familiar Logger contracts with features like:

• Localization. 
• Error codes. 
• Generated wiki documentation. 
• Separate audit, metric, security and debug logs. 

EELF is a facade, so logging output is configured in two ways:

1. By selection of a logging provider such as Logback or Log4j, typically via the classpath. 
2. By way of a provider configuration document, typically logback.xml or log4j.xml. See Providers.

SLF4J

SLF4J is a logging facade, and a humble masterpiece. It combines what's common to all major, modern Java logging providers into a single interface. This decouples the caller from the provider, and encourages the use of what's universal, familiar and proven. 

EELF also logs via SLF4J's abstractions.

Providers

Logging providers are normally enabled by their presence in the classpath. This means the decision may have been made for you, in some cases implicitly by dependencies. If you have a strong preference then you can change providers, but since the implementation is typically abstracted behind EELF or SLF4J, it may not be worth the effort.

Logback

Logback is the most commonly used provider. It is generally configured by an XML document named logback.xml. See Configuration.

Log4j 2.X

Log4j 2.X is somewhat less common than Logback, but equivalent. It is generally configured by an XML document named log4j.xml. See Configuration.

Log4j 1.X

Avoid, since 1.X is EOL, and since it does not support escaping, so its output may not be machine-readable. See https://logging.apache.org/log4j/1.2/.

This affects existing OpenDaylight-based components like SDNC and APPC, since ODL releases prior to Carbon bundle Log4j 1.X, and make it difficult to replace. The Common Controller SDK Project project targets ODL Carbon, so the problem should resolve in time.

What to Log

The purpose of logging is to capture diagnostic information.

An important aspect of this is analytics, which requires tracing of requests between components. In a large, distributed system such as ONAP this is critical to understanding behavior and performance. 

Messages, Levels, Components and Categories

It isn't the aim of this document to reiterate the basics, so advice here is general: 

• Use a logger. Consider using EELF. 
• Write log messages in English.
• Write meaningful messages. Consider what will be useful to consumers of logger output. 
• Use errorcodes to characterise exceptions.
• Log at the appropriate level. Be aware of the volume of logs that will be produced.
• Log in a machine-readable format. See Conventions.
• Log for analytics as well as troubleshooting.

Others have written extensively on this: 

• http://www.masterzen.fr/2013/01/13/the-10-commandments-of-logging/
• https://www.loggly.com/blog/how-to-write-effective-logs-for-remote-logging/
• And so on.

Context

TODO: more on the importance of transaction ID propagation.

MDCs

A Mapped Diagnostic Context (MDC) allows an arbitrary string-valued attribute to be attached to a Java thread. The MDC's value is then emitted with each log message. 

A good discussion of MDCs can be found at https://logback.qos.ch/manual/mdc.html. 

MDCs:

• Must be set as early in invocation as possible. 
• Must be unset on exit. 

Logging

Via SLF4J:

import java.util.UUID;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;
// ...
final Logger logger = LoggerFactory.getLogger(this.getClass());
MDC.put("SomeUUID", UUID.randomUUID().toString());
try {
    logger.info("This message will have a UUID-valued 'SomeUUID' MDC attached.");
    // ...
}
finally {
    MDC.clear();
}

EELF doesn't directly support MDCs, but SLF4J will receive any MDC that is set (where com.att.eelf.configuration.SLF4jWrapper is the configured EELF provider):

import java.util.UUID;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;
import com.att.eelf.configuration.EELFLogger;
import com.att.eelf.configuration.EELFManager;
// ...
final EELFLogger logger = EELFManager.getInstance().getLogger(this.getClass());
MDC.put("SomeUUID", UUID.randomUUID().toString());
try {
    logger.info("This message will have a UUID-valued 'SomeUUID' MDC attached.");
    // ...
}
finally {
    MDC.clear();
}

Serializing

Output of MDCs must ensure that:

• All reported MDCs are logged with both name AND value. Logging output should not treat any MDCs as special.
• All MDC names and values are escaped.

Escaping in Logback configuration can be achieved with:

%replace(%replace(%mdc){'\t','\\\\t'}){'\n','\\\\n'}

MDC - RequestID

This is often referred to by other names, including "Transaction ID", and one of several (pre-standardization) REST header names.

ONAP logging uses a universally unique "RequestID" value in log records to track the processing of each client request across all the ONAP components involved in its processing.

This value:

• Is logged as a RequestID MDC. 
• Is propagated between components in REST calls as an X-TransactionID HTTP header.

Receiving the X-TransactionID will vary by component according to APIs and frameworks. In general:

import javax.ws.rs.core.HttpHeaders;
// ...
final HttpHeaders headers = ...;
// ...
String txId = headers.getRequestHeaders().getFirst("X-TransactionID");
if (StringUtils.isBlank(txId)) {
	txId = UUID.randomUUID().toString();
}
MDC.put("RequestID", txID);

Setting the X-TransactionID likewise will vary. For example:

final String txID = MDC.get("RequestID");
HttpURLConnection cx = ...;
// ...
cx.setRequestProperty("X-TransactionID", txID);

MDC - InvocationID

InvocationID is similar to RequestID, but where RequestID correlates records relating a single, top-level invocation of ONAP as it traverses many systems, InvocationID correlates log entries relating to a single invocation of a single component. Typically this means via REST, but in certain cases an InvocationID may be allocated without a new invocation, e.g. when a request is retried.

RequestID and InvocationID allow an execution graph to be derived. This requires that:

• The relationship between RequestID and InvocationID is reported. 
• The relationship between caller and recipient is reported for each invocation.

The proposed approach is that:

• Callers:
  • Issue a new, unique InvocationID UUID for each downstream call they make. 
  • Log the new InvocationID, indicating the intent to invoke:
    • With Markers INVOKE, and SYNCHRONOUS if the invocation is synchronous.
    • With their own InvocationID still set as an MDC.
  • Pass the InvocationID as an X-InvocationID REST header.
• Invoked components:
  • Retrieve the InvocationID from REST headers upon invocation, or generate a UUID default. 
  • Set the InvocationID MDC.
  • Write a log entry with the Marker ENTRY. (In EELF this will be to the AUDIT log).
  • Act as per Callers in all downstream requests. 
  • Write a log entry with the Marker EXIT upon return. (In EELF this will be to the METRIC log).
  • Unset all MDCs on exit.

That seems onerous, but:

• It's only a few calls. 
• It can be largely abstracted in the case of EELF logging.

TODO: code.

MDCs - the Rest

Other MDCs are logged in a wide range of contexts.

Certain MDCs and their semantics may be specific to EELF log types.

TODO: cross-reference EELF output to v1 doc.

Examples

SDC-BE

20170907: audit.log

root@ip-172-31-93-160:/dockerdata-nfs/onap/sdc/logs/SDC/SDC-BE# tail -f audit.log
2017-09-07T18:04:03.679Z|||||qtp1013423070-72297||ASDC|SDC-BE|||||||N/A|INFO||||10.42.88.30||o.o.s.v.r.s.VendorLicenseModelsImpl||ActivityType=<audit>, Desc=< --Audit-- Create VLM. VLM Name: lm4>

Markers

Markers differ from MDCs in two important ways:

1. They have a name, but no value. They are a tag. 
2. Their scope is limited to logger calls which specifically reference them; they are not ThreadLocal. 

Logging

Via SLF4J:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
import org.slf4j.MarkerFactory;
// ...
final Logger logger = LoggerFactory.getLogger(this.getClass());
final Marker marker = MarkerFactory.getMarker("MY_MARKER");
logger.warn(marker, "This warning has a 'MY_MARKER' annotation.");

EELF does not allow Markers to be set directly. See notes on the InvocationID MDC.

Serializing

Marker names also need to be escaped, though they're much less likely to contain problematic characters than MDC values.

Escaping in Logback configuration can be achieved with:

%replace(%replace(%marker){'\t','\\\\t'}){'\n','\\\\n'}

Marker - ENTRY

This should be reported as early in invocation as possible, immediately after setting the RequestID and InvocationID MDCs.

It can be automatically set by EELF, and written to the AUDIT log. 

It must be manually set otherwise:

Marker - EXIT

This should be reported as late in invocation as possible, immediately before unsetting the RequestID and InvocationID MDCs.

It can be automatically reported by EELF, and written to the METRIC log. 

It must be manually set otherwise.

Marker - INVOKE

This should be reported by the caller of another ONAP component via REST, including a newly allocated InvocationID, which will be passed to the caller. 

TODO: EELF, without changing published APIs.

Marker - SYNCHRONOUS

This should accompany INVOKE when the invocation is synchronous.

TODO: EELF, without changing published APIs. 

Errorcodes

Errorcodes are reported as MDCs. 

Exceptions should be accompanied by an errrorcode. Typically this is achieved by incorporating errorcodes into your exception hierarchy and error handling. ONAP components generally do not share this kind of code, though EELF defines a marker interface (meaning it has no methods) EELFResolvableErrorEnum.

A common convention is for errorcodes to have two components:

1. A prefix, which identifies the origin of the error. 
2. A suffix, which identifies the kind of error.

Suffixes may be numeric or text. They may also be common to more than one component.

For example:

COMPONENT_X.STORAGE_ERROR

Output Format

Several considerations:

1. Logs should be human-readable (within reason). 
2. Shipper and indexing performance and durability depends on logs that can be parsed quickly and reliably.
3. Consistency means fewer shipping and indexing rules are required.

Text Output

ONAP needs to strike a balance between human-readable and machine-readable logs. This means:

• The use of tab as a delimiter.
• Escaping all messages, exceptions, MDC values, Markers, etc. to replace tabs in their content.
• Escaping all newlines with \n so that each entry is on one line. 

In logback, this looks like:

<property name="defaultPattern" value="%nopexception%logger
\t%date{yyyy-MM-dd'T'HH:mm:ss.SSSXXX,UTC}
\t%level
\t%replace(%replace(%message){'\t','\\\\t'}){'\n','\\\\n'}
\t%replace(%replace(%mdc){'\t','\\\\t'}){'\n','\\\\n'}
\t%replace(%replace(%rootException){'\t','\\\\t'}){'\n','\\\\n'}
\t%replace(%replace(%marker){'\t','\\\\t'}){'\n','\\\\n'}
\t%thread
\t%n"/>

The output of which, with MDCs, a Marker and a nested exception, with newlines added for readability looks like:

org.onap.example.component1.subcomponent1.LogbackTest
\t2017-08-06T16:09:03.594Z
\tERROR
\tHere's an error, that's usually bad
\tkey1=value1, key2=value2 with space, key5=value5"with"quotes, key3=value3\nwith\nnewlines, key4=value4\twith\ttabs
\tjava.lang.RuntimeException: Here's Johnny
\n\tat org.onap.example.component1.subcomponent1.LogbackTest.main(LogbackTest.java:24)
\nWrapped by: java.lang.RuntimeException: Little pigs, little pigs, let me come in
\n\tat org.onap.example.component1.subcomponent1.LogbackTest.main(LogbackTest.java:27)
\tAMarker1
\tmain     

Default Logstash indexing rules understand output in this format.

XML Output

For Log4j 1.X output, since escaping is not supported, the best alternative is to emit logs in XML format. 

There may be other instances where XML (or JSON) output may be desirable. Default indexing rules support 

Default Logstash indexing rules understand the XML output of Log4J's XMLLayout.

Output Location

Standardization of output locations makes logs easier to locate and ship for indexing. 

Logfiles should default to beneath /var/log, and beneath /var/log/ONAP in the case of core ONAP components:

/var/log/ONAP/<component>[/<subcomponent>]/*.log

Configuration

Logging providers should be configured by file. Files should be at a predictable, static location, so that they can be written by deployment automation. Ideally this should be under /etc/ONAP, but compliance is low.

Locations

All logger provider configuration document locations namespaced by component and (if applicable) subcomponent by default:

/etc/onap/<component>[/<subcomponent>]/<provider>.xml

Where <provider>.xml, will typically be one of:

1. logback.xml
2. log4j.xml
3. log4j.properties

Reconfiguration

Logger providers should reconfigure themselves automatically when their configuration file is rewritten. All major providers should support this. 

The default interval is 10s. 

Overrides

The location of the configuration file MAY be overrideable, for example by an environment variable, but this is left for individual components to decide. 

Archetypes

Configuration archetypes can be found in the ONAP codebase. Choose according to your provider, and whether you're logging via EELF. Efforts to standardize them are underway, so the ones you should be looking for are where tab is used as a separator. (Previously it was "|").

Retention

Logfiles are often large. Logging providers allow retention policies to be configured. 

Retention has to balance:

• The need to index logs before they're removed. 
• The need to retain logs for other (including regulatory) purposes. 

Defaults are subject to change. Currently they are:

1. Files <= 50MB before rollover. 
2. Files retain for 30 days. 
3. Total files capped at 10GB. 

In Logback configuration XML:

<appender name="file" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${outputDirectory}/${outputFilename}.log</file>
    <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
        <fileNamePattern>${outputDirectory}/${outputFilename}.%d{yyyy-MM-dd}.%i.log.zip</fileNamePattern>
        <maxFileSize>50MB</maxFileSize>
        <maxHistory>30</maxHistory>
        <totalSizeCap>10GB</totalSizeCap>
    </rollingPolicy>
    <encoder>
        <!-- ... -->
    </encoder>
</appender>

Types of EELF Logs

EELF guidelines stipulate that an application should output log records to four separate files:

1. audit
2. metric
3. error
4. debug

This applies only to EELF logging. Components which log directly to a provider may choose to emit the same set of logs, but most do not. 

Audit Log

An audit log is required for EELF-enabled components, and provides a summary view of the processing of a (e.g., transaction) request within an application. It captures activity requests that are received by an ONAP component, and includes such information as the time the activity is initiated, then it finishes, and the API that is invoked at the component.

Audit log records are intended to capture the high level view of activity within an ONAP component. Specifically, an API request handled by an ONAP component is reflected in a single Audit log record that captures the time the request was received, the time that processing was completed, as well as other information about the API request (e.g., API name, on whose behalf it was invoked, etc).

Metric Log

A metric log is required for EELF-enabled components, and provides a more detailed view into the processing of a transaction within an application. It captures the beginning and ending of activities needed to complete it. These can include calls to or interactions with other ONAP or non-ONAP entities.

Suboperations invoked as part of the processing of the API request are logged in the Metrics log. For example, when a call is made to another ONAP component or external (i.e., non-ONAP) entity, a Metrics log record captures that call. In such a case, the Metrics log record indicates (among other things) the time the call is made, when it returns, the entity that is called, and the API invoked on that entity. The Metrics log record contain the same RequestID as the Audit log record so the two can be correlated.

Note that a single request may result in multiple Audit log records at an ONAP component and may result in multiple Metrics log records generated by the component when multiple suboperations are required to satisfy the API request captured in the Audit log record.

Error Log

An error log is required for EELF-enabled components, and is intended to capture info, warn, error and fatal conditions sensed (“exception handled”) by the software components.

Debug Log

A debug log is optional for EELF-enabled components, and is intended to capture whatever data may be needed to debug and correct abnormal conditions of the application.

Engine.out

Console logging may also be present, and is intended to capture “system/infrastructure” records. That is stdout and stderr assigned to a single “engine.out” file in a directory configurable (e.g. as an environment/shell variable) by operations personnel.

New ONAP Component Checklist

By following a few simple rules:

• Your component's output will be indexed automatically. 
• Analytics will be able to trace invocation through your component.

Obligations fall into two categories:

1. Conventions regarding configuration, line format and output. 
2. Ensuring the propagation of contextual information. 

You must:

1. Choose a Logging provider and/or EELF. Decisions, decisions.
2. Create a configuration file based on an existing archetype. See Configuration.
3. Read your configuration file when your components initialize logging.
4. Write logs to a standard location so that they can be shipped by Filebeat for indexing. See Output Location.
5. Report transaction state:
   1. Retrieve, default and propagate RequestID. See MDC - RequestID.
   2. At each invocation of one ONAP component by another:
      1. Initialize and propagate InvocationID. See MDC - Invocation ID.
      2. Report INVOKE and SYNCHRONOUS markers in caller. 
      3. Report ENTRY and EXIT markers in recipient. 
6. Write useful logs!