The GrokReader Controller Service provides a means for parsing and structuring input that is made up of unstructured text, such as log files. Grok allows users to add a naming construct to Regular Expressions such that they can be composed in order to create expressions that are easier to manage and work with. This Controller Service consists of one Required Property and a few Optional Properties. The is named Grok Pattern File property specifies the filename of a file that contains Grok Patterns that can be used for parsing log data. If not specified, a default patterns file will be used. Its contents are provided below. There are also properties for specifying the schema to use when parsing data. The schema is not required. However, when data is parsed a Record is created that contains all of the fields present in the Grok Expression (explained below), and all fields are of type String. If a schema is chosen, the field can be declared to be a different, compatible type, such as number. Additionally, if the schema does not contain one of the fields in the parsed data, that field will be ignored. This can be used to filter out fields that are not of interest.

The Required Property is named Grok Expression and specifies how to parse each incoming record. This is done by providing a Grok Expression such as: %{TIMESTAMP_ISO8601:timestamp} %{LOGLEVEL:level} \[%{DATA:thread}\] %{DATA:class} %{GREEDYDATA:message}. This Expression will parse Apache NiFi log messages. This is accomplished by specifying that a line begins with the TIMESTAMP_ISO8601 pattern (which is a Regular Expression defined in the default Grok Patterns File). The value that matches this pattern is then given the name timestamp. As a result, the value that matches this pattern will be assigned to a field named timestamp in the Record that produced by this Controller Service.

If a line is encountered in the FlowFile that does not match the configured Grok Expression, it is assumed that the line is part of the previous message. If the line is the start of a stack trace, then the entire stack trace is read in and assigned to a field named STACK_TRACE. Otherwise, the line is appended to the last field defined in the Grok Expression. This is done because typically the last field is a 'message' type of field, which can consist of new-lines.

Schemas and Type Coercion

When a record is parsed from incoming data, it is separated into fields. Each of these fields is then looked up against the configured schema (by field name) in order to determine what the type of the data should be. If the field is not present in the schema, that field is omitted from the Record. If the field is found in the schema, the data type of the received data is compared against the data type specified in the schema. If the types match, the value of that field is used as-is. If the schema indicates that the field should be of a different type, then the Controller Service will attempt to coerce the data into the type specified by the schema. If the field cannot be coerced into the specified type, an Exception will be thrown.

The following rules apply when attempting to coerce a field value from one data type to another:

If none of the above rules apply when attempting to coerce a value from one data type to another, the coercion will fail and an Exception will be thrown.

Examples

As an example, consider that this Controller Service is configured with the following properties:

Property Name Property Value
Grok Expression %{TIMESTAMP_ISO8601:timestamp} %{LOGLEVEL:level} \[%{DATA:thread}\] %{DATA:class} %{GREEDYDATA:message}

Additionally, let's consider a FlowFile whose contents consists of the following:

2016-08-04 13:26:32,473 INFO [Leader Election Notification Thread-1] o.a.n.c.l.e.CuratorLeaderElectionManager org.apache.nifi.controller.leader.election.CuratorLeaderElectionManager$ElectionListener@1fa27ea5 has been interrupted; no longer leader for role 'Cluster Coordinator'
2016-08-04 13:26:32,474 ERROR [Leader Election Notification Thread-2] o.apache.nifi.controller.FlowController One
Two
Three
org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_45]
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_45]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_45]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_45]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
        at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
Caused by: org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    ... 12 common frames omitted
2016-08-04 13:26:35,475 WARN [Curator-Framework-0] org.apache.curator.ConnectionState Connection attempt unsuccessful after 3008 (greater than max timeout of 3000). Resetting connection and trying again with a new connection.
        

In this case, the result will be that this FlowFile consists of 3 different records. The first record will contain the following values:

Field Name Field Value
timestamp 2016-08-04 13:26:32,473
level INFO
thread Leader Election Notification Thread-1
class o.a.n.c.l.e.CuratorLeaderElectionManager
message org.apache.nifi.controller.leader.election.CuratorLeaderElectionManager$ElectionListener@1fa27ea5 has been interrupted; no longer leader for role 'Cluster Coordinator'
STACK_TRACE null

The second record will contain the following values:

Field Name Field Value
timestamp 2016-08-04 13:26:32,474
level ERROR
thread Leader Election Notification Thread-2
class o.apache.nifi.controller.FlowController
message One
Two
Three
STACK_TRACE
org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_45]
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_45]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_45]
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_45]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
        at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
Caused by: org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
    ... 12 common frames omitted

The third record will contain the following values:

Field Name Field Value
timestamp 2016-08-04 13:26:35,475
level WARN
thread Curator-Framework-0
class org.apache.curator.ConnectionState
message Connection attempt unsuccessful after 3008 (greater than max timeout of 3000). Resetting connection and trying again with a new connection.
STACK_TRACE null

Default Patterns

The following patterns are available in the default Grok Pattern File:

# Log Levels
LOGLEVEL ([Aa]lert|ALERT|[Tt]race|TRACE|[Dd]ebug|DEBUG|[Nn]otice|NOTICE|[Ii]nfo|INFO|[Ww]arn?(?:ing)?|WARN?(?:ING)?|[Ee]rr?(?:or)?|ERR?(?:OR)?|[Cc]rit?(?:ical)?|CRIT?(?:ICAL)?|[Ff]atal|FATAL|[Ss]evere|SEVERE|EMERG(?:ENCY)?|[Ee]merg(?:ency)?)|FINE|FINER|FINEST|CONFIG

# Syslog Dates: Month Day HH:MM:SS
SYSLOGTIMESTAMP %{MONTH} +%{MONTHDAY} %{TIME}
PROG (?:[\w._/%-]+)
SYSLOGPROG %{PROG:program}(?:\[%{POSINT:pid}\])?
SYSLOGHOST %{IPORHOST}
SYSLOGFACILITY <%{NONNEGINT:facility}.%{NONNEGINT:priority}>
HTTPDATE %{MONTHDAY}/%{MONTH}/%{YEAR}:%{TIME} %{INT}

# Months: January, Feb, 3, 03, 12, December
MONTH \b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|Nov(?:ember)?|Dec(?:ember)?)\b
MONTHNUM (?:0?[1-9]|1[0-2])
MONTHNUM2 (?:0[1-9]|1[0-2])
MONTHDAY (?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9])

# Days: Monday, Tue, Thu, etc...
DAY (?:Mon(?:day)?|Tue(?:sday)?|Wed(?:nesday)?|Thu(?:rsday)?|Fri(?:day)?|Sat(?:urday)?|Sun(?:day)?)

# Years?
YEAR (?>\d\d){1,2}
HOUR (?:2[0123]|[01]?[0-9])
MINUTE (?:[0-5][0-9])
# '60' is a leap second in most time standards and thus is valid.
SECOND (?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)
TIME (?!<[0-9])%{HOUR}:%{MINUTE}(?::%{SECOND})(?![0-9])

# datestamp is YYYY/MM/DD-HH:MM:SS.UUUU (or something like it)
DATE_US_MONTH_DAY_YEAR %{MONTHNUM}[/-]%{MONTHDAY}[/-]%{YEAR}
DATE_US_YEAR_MONTH_DAY %{YEAR}[/-]%{MONTHNUM}[/-]%{MONTHDAY}
DATE_US %{DATE_US_MONTH_DAY_YEAR}|%{DATE_US_YEAR_MONTH_DAY}
DATE_EU %{MONTHDAY}[./-]%{MONTHNUM}[./-]%{YEAR}
ISO8601_TIMEZONE (?:Z|[+-]%{HOUR}(?::?%{MINUTE}))
ISO8601_SECOND (?:%{SECOND}|60)
TIMESTAMP_ISO8601 %{YEAR}-%{MONTHNUM}-%{MONTHDAY}[T ]%{HOUR}:?%{MINUTE}(?::?%{SECOND})?%{ISO8601_TIMEZONE}?
DATE %{DATE_US}|%{DATE_EU}
DATESTAMP %{DATE}[- ]%{TIME}
TZ (?:[PMCE][SD]T|UTC)
DATESTAMP_RFC822 %{DAY} %{MONTH} %{MONTHDAY} %{YEAR} %{TIME} %{TZ}
DATESTAMP_RFC2822 %{DAY}, %{MONTHDAY} %{MONTH} %{YEAR} %{TIME} %{ISO8601_TIMEZONE}
DATESTAMP_OTHER %{DAY} %{MONTH} %{MONTHDAY} %{TIME} %{TZ} %{YEAR}
DATESTAMP_EVENTLOG %{YEAR}%{MONTHNUM2}%{MONTHDAY}%{HOUR}%{MINUTE}%{SECOND}


POSINT \b(?:[1-9][0-9]*)\b
NONNEGINT \b(?:[0-9]+)\b
WORD \b\w+\b
NOTSPACE \S+
SPACE \s*
DATA .*?
GREEDYDATA .*
QUOTEDSTRING (?>(?"(?>\\.|[^\\"]+)+"|""|(?>'(?>\\.|[^\\']+)+')|''|(?>`(?>\\.|[^\\`]+)+`)|``))
UUID [A-Fa-f0-9]{8}-(?:[A-Fa-f0-9]{4}-){3}[A-Fa-f0-9]{12}

USERNAME [a-zA-Z0-9._-]+
USER %{USERNAME}
INT (?:[+-]?(?:[0-9]+))
BASE10NUM (?[+-]?(?:(?:[0-9]+(?:\.[0-9]+)?)|(?:\.[0-9]+)))
NUMBER (?:%{BASE10NUM})
BASE16NUM (?/(?>[\w_%!$@:.,-]+|\\.)*)+
TTY (?:/dev/(pts|tty([pq])?)(\w+)?/?(?:[0-9]+))
WINPATH (?>[A-Za-z]+:|\\)(?:\\[^\\?*]*)+
URIPROTO [A-Za-z]+(\+[A-Za-z+]+)?
URIHOST %{IPORHOST}(?::%{POSINT:port})?
# uripath comes loosely from RFC1738, but mostly from what Firefox
# doesn't turn into %XX
URIPATH (?:/[A-Za-z0-9$.+!*'(){},~:;=@#%_\-]*)+
#URIPARAM \?(?:[A-Za-z0-9]+(?:=(?:[^&]*))?(?:&(?:[A-Za-z0-9]+(?:=(?:[^&]*))?)?)*)?
URIPARAM \?[A-Za-z0-9$.+!*'|(){},~@#%&/=:;_?\-\[\]]*
URIPATHPARAM %{URIPATH}(?:%{URIPARAM})?
URI %{URIPROTO}://(?:%{USER}(?::[^@]*)?@)?(?:%{URIHOST})?(?:%{URIPATHPARAM})?

# Shortcuts
QS %{QUOTEDSTRING}

# Log formats
SYSLOGBASE %{SYSLOGTIMESTAMP:timestamp} (?:%{SYSLOGFACILITY} )?%{SYSLOGHOST:logsource} %{SYSLOGPROG}:
COMMONAPACHELOG %{IPORHOST:clientip} %{USER:ident} %{USER:auth} \[%{HTTPDATE:timestamp}\] "(?:%{WORD:verb} %{NOTSPACE:request}(?: HTTP/%{NUMBER:httpversion})?|%{DATA:rawrequest})" %{NUMBER:response} (?:%{NUMBER:bytes}|-)
COMBINEDAPACHELOG %{COMMONAPACHELOG} %{QS:referrer} %{QS:agent}