Flink 1.11 之前
在 Flink 1.11 之前，Flink 使用的日志是 Log4j，配置文件 log4j.properties 中的内容如下：
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, file
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
# Log all infos in the given file
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.file=${log.file}
log4j.appender.file.append=false
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, file
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, file
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
# Log all infos in the given file
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.file=${log.file}
log4j.appender.file.append=false
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, file该配置文件会将 JobManager 和 TaskManager 的日志分别打印在不同的文件中，每个文件的日志大小一直会增加，如果想配置日志文件按大小滚动的话可以使用 RollingFileAppender，则要将配置文件改成如下：
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, RFA
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
log4j.appender.RFA=org.apache.log4j.RollingFileAppender
log4j.appender.RFA.File=${log.file}
log4j.appender.RFA.MaxFileSize=256MB
log4j.appender.RFA.Append=true
log4j.appender.RFA.MaxBackupIndex=10
log4j.appender.RFA.layout=org.apache.log4j.PatternLayout
log4j.appender.RFA.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %t %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, RFA
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, RFA
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
log4j.appender.RFA=org.apache.log4j.RollingFileAppender
log4j.appender.RFA.File=${log.file}
log4j.appender.RFA.MaxFileSize=256MB
log4j.appender.RFA.Append=true
log4j.appender.RFA.MaxBackupIndex=10
log4j.appender.RFA.layout=org.apache.log4j.PatternLayout
log4j.appender.RFA.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %t %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, RFA为什么要在生产环境下将日志文件改成按照大小滚动呢？
无非是在生产情况下，流数据是非常大的，有的时候自己可能会通过 print() 打印出来流数据进来验证结果，有的时候可能是打印的日志记录做 debug 用，然后到生产忘记关了，结果到生产就全部将流数据打印出来，这种情况下，就会导致 TaskManager 的日志文件会非常大，那么我们打开 Web UI 查看可能就会很卡，这也就是为啥我们有时候打开 Web UI 查看日志的时候，非常卡顿，加载不出来的原因了，主要原因就是日志文件太大导致的。
当然有的同学可能会想着将 Flink 作业的日志发到 Kafka 做统一的收集，然后做一些日志分析告警和再消费发到 ElasticSearch 等去做日志搜索，如果是发到 Kafka，可以使用 KafkaLog4jAppender，日志文件配置如下：
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, kafka
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
# log send to kafka
log4j.appender.kafka=org.apache.kafka.log4jappender.KafkaLog4jAppender
log4j.appender.kafka.brokerList=localhost:9092
log4j.appender.kafka.topic=flink_logs
log4j.appender.kafka.compressionType=none
log4j.appender.kafka.requiredNumAcks=0
log4j.appender.kafka.syncSend=false
log4j.appender.kafka.layout=org.apache.log4j.PatternLayout
log4j.appender.kafka.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
log4j.appender.kafka.level=INFO
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, kafka
# This affects logging for both user code and Flink
log4j.rootLogger=INFO, kafka
# Uncomment this if you want to _only_ change Flink's logging
#log4j.logger.org.apache.flink=INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
log4j.logger.akka=INFO
log4j.logger.org.apache.kafka=INFO
log4j.logger.org.apache.hadoop=INFO
log4j.logger.org.apache.zookeeper=INFO
# log send to kafka
log4j.appender.kafka=org.apache.kafka.log4jappender.KafkaLog4jAppender
log4j.appender.kafka.brokerList=localhost:9092
log4j.appender.kafka.topic=flink_logs
log4j.appender.kafka.compressionType=none
log4j.appender.kafka.requiredNumAcks=0
log4j.appender.kafka.syncSend=false
log4j.appender.kafka.layout=org.apache.log4j.PatternLayout
log4j.appender.kafka.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
log4j.appender.kafka.level=INFO
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
log4j.logger.org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline=ERROR, kafkaFlink 1.11
在 Flink 1.11 中，将 Log4j 升级到了 Log4j2，可以通过查看 FLINK-15672 可以知道变更的文件很多，
新版本的日志配置文件还是叫 log4j.properties，配置如下所示，不清楚为啥 FLINK-15672 代码提交中改了很多地方的配置文件名为 log4j2.properties，但是 Flink 最后打包的 conf 目录下还是保持和之前一样的文件名，按道理不是也应该进行更改成 log4j2.properties 的吗？
# This affects logging for both user code and Flink
rootLogger.level = INFO
rootLogger.appenderRef.file.ref = MainAppender
# Uncomment this if you want to _only_ change Flink's logging
# = org.apache.flink
#logger.flink.level = INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
= akka
logger.akka.level = INFO
= org.apache.kafka
logger.kafka.level = INFO
= org.apache.hadoop
logger.hadoop.level = INFO
= org.apache.zookeeper
logger.zookeeper.level = INFO
# Log all infos in the given file
= MainAppender
appender.main.type = File
appender.main.append = false
appender.main.fileName = ${sys:log.file}
appender.main.layout.type = PatternLayout
appender.main.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
= org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline
logger.netty.level = OFF
# This affects logging for both user code and Flink
rootLogger.level = INFO
rootLogger.appenderRef.file.ref = MainAppender
# Uncomment this if you want to _only_ change Flink's logging
# = org.apache.flink
#logger.flink.level = INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
= akka
logger.akka.level = INFO
= org.apache.kafka
logger.kafka.level = INFO
= org.apache.hadoop
logger.hadoop.level = INFO
= org.apache.zookeeper
logger.zookeeper.level = INFO
# Log all infos in the given file
= MainAppender
appender.main.type = File
appender.main.append = false
appender.main.fileName = ${sys:log.file}
appender.main.layout.type = PatternLayout
appender.main.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
= org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline
logger.netty.level = OFF默认这个配置也是不会对日志文件进行按照大小滚动的，那么如果我们要保持和之前的效果一样(按照日志大小滚动日志文件)该怎么做呢？你可以更改配置文件的内容如下所示：
# This affects logging for both user code and Flink
rootLogger.level = INFO
rootLogger.appenderRef.rolling.ref = RollingFileAppender
# Uncomment this if you want to _only_ change Flink's logging
# = org.apache.flink
#logger.flink.level = INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
= akka
logger.akka.level = INFO
= org.apache.kafka
logger.kafka.level = INFO
= org.apache.hadoop
logger.hadoop.level = INFO
= org.apache.zookeeper
logger.zookeeper.level = INFO
# Log all infos in the given rolling file
= RollingFileAppender
appender.rolling.type = RollingFile
appender.rolling.append = false
appender.rolling.fileName = ${sys:log.file}
appender.rolling.filePattern = ${sys:log.file}.%i
appender.rolling.layout.type = PatternLayout
appender.rolling.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
appender.rolling.policies.type = Policies
appender.rolling.policies.size.type = SizeBasedTriggeringPolicy
appender.rolling.policies.size.size = 200MB
appender.rolling.strategy.type = DefaultRolloverStrategy
appender.rolling.strategy.max = 10
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
= org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline
logger.netty.level = OFF
# This affects logging for both user code and Flink
rootLogger.level = INFO
rootLogger.appenderRef.rolling.ref = RollingFileAppender
# Uncomment this if you want to _only_ change Flink's logging
# = org.apache.flink
#logger.flink.level = INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
= akka
logger.akka.level = INFO
= org.apache.kafka
logger.kafka.level = INFO
= org.apache.hadoop
logger.hadoop.level = INFO
= org.apache.zookeeper
logger.zookeeper.level = INFO
# Log all infos in the given rolling file
= RollingFileAppender
appender.rolling.type = RollingFile
appender.rolling.append = false
appender.rolling.fileName = ${sys:log.file}
appender.rolling.filePattern = ${sys:log.file}.%i
appender.rolling.layout.type = PatternLayout
appender.rolling.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
appender.rolling.policies.type = Policies
appender.rolling.policies.size.type = SizeBasedTriggeringPolicy
appender.rolling.policies.size.size = 200MB
appender.rolling.strategy.type = DefaultRolloverStrategy
appender.rolling.strategy.max = 10
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
= org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline
logger.netty.level = OFF如果你升级了到 1.11 版本，不能继续延用之前 1.11 之前的配置的那种日志文件滚动的配置了，需要做点变更。上面配置的表示日志文件以每隔 200MB 会进行切分，然后日志切分后的文件名是 ${sys:log.file}.%i，以数字结尾。
1.11 进行了配置厚度的效果如下图所示：
TaskManager 日志列表展示
JobManager 日志列表展示
从上面图中可以发现 1.11 对于查看日志比之前友好了不少，多个日志文件都有列表展示，而不再是之前只能查看单个日志文件了。
注：为了演示日志文件滚动的效果，测试的时候设置的日志 appender.rolling.policies.size.size 是 1KB
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