Multiline

The Multiline Filter helps to concatenate messages that originally belong to one context but were split across multiple records or log lines. Common examples are stack traces or applications that print logs in multiple lines. 
As part of the built-in functionality, without major configuration effort, you can enable one of ours built-in parsers with auto detection and multi format support:
go
python
ruby
java (Google Cloud Platform Java stacktrace format)
Some comments about this filter:
The usage of this filter depends on a previous configuration of a Multiline Parser definition. 
If you aim to concatenate messages split originally by Docker or CRI container engines, we recommend doing the concatenation on Tail plugin,  this same functionality exists there.
This filter does not perform buffering that persists across different Chunks. This filter process one Chunk at a time and is not suitable for sources that might send multiline messages in separated chunks. 
For cases where Multiline mode is required and the source plugin does not support it, please file a Github Enhancement with such requirement and specific details of the use case.
Configuration Parameters
The plugin supports the following configuration parameters:
Property
Description
multiline.parser
Specify one or multiple Multiline Parser definitions to apply to the content. You can specify multiple multiline parsers to detect different formats by separating them with a comma. 
multiline.key_content
Key name that holds the content to process. Note that a Multiline Parser definition can already specify the key_content to use, but this option allows to overwrite that value for the purpose of the filter.
Configuration Example
The following example aims to parse a log file called test.log that contains some full lines, a custom Java stacktrace and a Go stacktrace. 
The following example files can be located at:

https://github.com/fluent/fluent-bit/tree/master/documentation/examples/multiline/filter_multiline​
Example files content:
fluent-bit.conf
parsers_multiline.conf
test.log
This is the primary Fluent Bit configuration file. It includes the parsers_multiline.conf and tails the file test.log by applying the multiline parsers multiline-regex-test and go. Then it sends the processing to the standard output. 
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[SERVICE]
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    flush                 1
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    log_level             info
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    parsers_file          parsers_multiline.conf
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​
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[INPUT]
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    name                  tail
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    path                  test.log
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    read_from_head        true
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​
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[FILTER]
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    name                  multiline
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    match                 *
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    multiline.key_content log
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    multiline.parser      go, multiline-regex-test
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​
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[OUTPUT]
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    name                  stdout
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    match                 *
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This second file defines a multiline parser for the example. Note that a second multiline parser called go is used in fluent-bit.conf, but this one is a built-in parser.
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[MULTILINE_PARSER]
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    name          multiline-regex-test
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    type          regex
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    flush_timeout 1000
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    #
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    # Regex rules for multiline parsing
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    # ---------------------------------
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    #
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    # configuration hints:
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    #
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    #  - first state always has the name: start_state
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    #  - every field in the rule must be inside double quotes
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    #
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    # rules |   state name  | regex pattern                  | next state
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    # ------|---------------|--------------------------------------------
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    rule      "start_state"   "/(Dec \d+ \d+\:\d+\:\d+)(.*)/"  "cont"
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    rule      "cont"          "/^\s+at.*/"                     "cont"
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An example file with multiline and multiformat content:
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single line...
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Dec 14 06:41:08 Exception in thread "main" java.lang.RuntimeException: Something has gone wrong, aborting!
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    at com.myproject.module.MyProject.badMethod(MyProject.java:22)
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    at com.myproject.module.MyProject.oneMoreMethod(MyProject.java:18)
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    at com.myproject.module.MyProject.anotherMethod(MyProject.java:14)
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    at com.myproject.module.MyProject.someMethod(MyProject.java:10)
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    at com.myproject.module.MyProject.main(MyProject.java:6)
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another line...
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panic: my panic
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​
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goroutine 4 [running]:
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panic(0x45cb40, 0x47ad70)
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  /usr/local/go/src/runtime/panic.go:542 +0x46c fp=0xc42003f7b8 sp=0xc42003f710 pc=0x422f7c
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main.main.func1(0xc420024120)
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  foo.go:6 +0x39 fp=0xc42003f7d8 sp=0xc42003f7b8 pc=0x451339
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003f7e0 sp=0xc42003f7d8 pc=0x44b4d1
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created by main.main
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  foo.go:5 +0x58
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​
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goroutine 1 [chan receive]:
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runtime.gopark(0x4739b8, 0xc420024178, 0x46fcd7, 0xc, 0xc420028e17, 0x3)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc420053e30 sp=0xc420053e00 pc=0x42503c
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runtime.goparkunlock(0xc420024178, 0x46fcd7, 0xc, 0x1000f010040c217, 0x3)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc420053e70 sp=0xc420053e30 pc=0x42512e
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runtime.chanrecv(0xc420024120, 0x0, 0xc420053f01, 0x4512d8)
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  /usr/local/go/src/runtime/chan.go:506 +0x304 fp=0xc420053f20 sp=0xc420053e70 pc=0x4046b4
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runtime.chanrecv1(0xc420024120, 0x0)
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  /usr/local/go/src/runtime/chan.go:388 +0x2b fp=0xc420053f50 sp=0xc420053f20 pc=0x40439b
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main.main()
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  foo.go:9 +0x6f fp=0xc420053f80 sp=0xc420053f50 pc=0x4512ef
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runtime.main()
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  /usr/local/go/src/runtime/proc.go:185 +0x20d fp=0xc420053fe0 sp=0xc420053f80 pc=0x424bad
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc420053fe8 sp=0xc420053fe0 pc=0x44b4d1
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​
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goroutine 2 [force gc (idle)]:
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runtime.gopark(0x4739b8, 0x4ad720, 0x47001e, 0xf, 0x14, 0x1)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc42003e768 sp=0xc42003e738 pc=0x42503c
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runtime.goparkunlock(0x4ad720, 0x47001e, 0xf, 0xc420000114, 0x1)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc42003e7a8 sp=0xc42003e768 pc=0x42512e
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runtime.forcegchelper()
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  /usr/local/go/src/runtime/proc.go:238 +0xcc fp=0xc42003e7e0 sp=0xc42003e7a8 pc=0x424e5c
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003e7e8 sp=0xc42003e7e0 pc=0x44b4d1
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created by runtime.init.4
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  /usr/local/go/src/runtime/proc.go:227 +0x35
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​
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goroutine 3 [GC sweep wait]:
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runtime.gopark(0x4739b8, 0x4ad7e0, 0x46fdd2, 0xd, 0x419914, 0x1)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc42003ef60 sp=0xc42003ef30 pc=0x42503c
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runtime.goparkunlock(0x4ad7e0, 0x46fdd2, 0xd, 0x14, 0x1)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc42003efa0 sp=0xc42003ef60 pc=0x42512e
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runtime.bgsweep(0xc42001e150)
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  /usr/local/go/src/runtime/mgcsweep.go:52 +0xa3 fp=0xc42003efd8 sp=0xc42003efa0 pc=0x419973
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003efe0 sp=0xc42003efd8 pc=0x44b4d1
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created by runtime.gcenable
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  /usr/local/go/src/runtime/mgc.go:216 +0x58
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one more line, no multiline
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​
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By running Fluent Bit with the given configuration file you will obtain:
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$ fluent-bit -c fluent-bit.conf 
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​
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[0] tail.0: [1626736433.143567481, {"log"=>"single line..."}]
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[1] tail.0: [1626736433.143570538, {"log"=>"Dec 14 06:41:08 Exception in thread "main" java.lang.RuntimeException: Something has gone wrong, aborting!
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    at com.myproject.module.MyProject.badMethod(MyProject.java:22)
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    at com.myproject.module.MyProject.oneMoreMethod(MyProject.java:18)
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    at com.myproject.module.MyProject.anotherMethod(MyProject.java:14)
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    at com.myproject.module.MyProject.someMethod(MyProject.java:10)
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    at com.myproject.module.MyProject.main(MyProject.java:6)"}]
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[2] tail.0: [1626736433.143572538, {"log"=>"another line..."}]
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[3] tail.0: [1626736433.143572894, {"log"=>"panic: my panic
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​
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goroutine 4 [running]:
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panic(0x45cb40, 0x47ad70)
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  /usr/local/go/src/runtime/panic.go:542 +0x46c fp=0xc42003f7b8 sp=0xc42003f710 pc=0x422f7c
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main.main.func1(0xc420024120)
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  foo.go:6 +0x39 fp=0xc42003f7d8 sp=0xc42003f7b8 pc=0x451339
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003f7e0 sp=0xc42003f7d8 pc=0x44b4d1
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created by main.main
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  foo.go:5 +0x58
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​
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goroutine 1 [chan receive]:
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runtime.gopark(0x4739b8, 0xc420024178, 0x46fcd7, 0xc, 0xc420028e17, 0x3)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc420053e30 sp=0xc420053e00 pc=0x42503c
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runtime.goparkunlock(0xc420024178, 0x46fcd7, 0xc, 0x1000f010040c217, 0x3)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc420053e70 sp=0xc420053e30 pc=0x42512e
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runtime.chanrecv(0xc420024120, 0x0, 0xc420053f01, 0x4512d8)
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  /usr/local/go/src/runtime/chan.go:506 +0x304 fp=0xc420053f20 sp=0xc420053e70 pc=0x4046b4
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runtime.chanrecv1(0xc420024120, 0x0)
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  /usr/local/go/src/runtime/chan.go:388 +0x2b fp=0xc420053f50 sp=0xc420053f20 pc=0x40439b
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main.main()
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  foo.go:9 +0x6f fp=0xc420053f80 sp=0xc420053f50 pc=0x4512ef
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runtime.main()
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  /usr/local/go/src/runtime/proc.go:185 +0x20d fp=0xc420053fe0 sp=0xc420053f80 pc=0x424bad
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc420053fe8 sp=0xc420053fe0 pc=0x44b4d1
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​
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goroutine 2 [force gc (idle)]:
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runtime.gopark(0x4739b8, 0x4ad720, 0x47001e, 0xf, 0x14, 0x1)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc42003e768 sp=0xc42003e738 pc=0x42503c
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runtime.goparkunlock(0x4ad720, 0x47001e, 0xf, 0xc420000114, 0x1)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc42003e7a8 sp=0xc42003e768 pc=0x42512e
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runtime.forcegchelper()
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  /usr/local/go/src/runtime/proc.go:238 +0xcc fp=0xc42003e7e0 sp=0xc42003e7a8 pc=0x424e5c
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003e7e8 sp=0xc42003e7e0 pc=0x44b4d1
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created by runtime.init.4
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  /usr/local/go/src/runtime/proc.go:227 +0x35
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​
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goroutine 3 [GC sweep wait]:
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runtime.gopark(0x4739b8, 0x4ad7e0, 0x46fdd2, 0xd, 0x419914, 0x1)
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  /usr/local/go/src/runtime/proc.go:280 +0x12c fp=0xc42003ef60 sp=0xc42003ef30 pc=0x42503c
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runtime.goparkunlock(0x4ad7e0, 0x46fdd2, 0xd, 0x14, 0x1)
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  /usr/local/go/src/runtime/proc.go:286 +0x5e fp=0xc42003efa0 sp=0xc42003ef60 pc=0x42512e
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runtime.bgsweep(0xc42001e150)
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  /usr/local/go/src/runtime/mgcsweep.go:52 +0xa3 fp=0xc42003efd8 sp=0xc42003efa0 pc=0x419973
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runtime.goexit()
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  /usr/local/go/src/runtime/asm_amd64.s:2337 +0x1 fp=0xc42003efe0 sp=0xc42003efd8 pc=0x44b4d1
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created by runtime.gcenable
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  /usr/local/go/src/runtime/mgc.go:216 +0x58"}]
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[4] tail.0: [1626736433.143585473, {"log"=>"one more line, no multiline"}]
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​
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The lines that did not match a pattern are not considered as part of the multiline message, while the ones that matched the rules were concatenated properly.

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Contents

Configuration Parameters

Configuration Example