Logging Options on YARN
Describes the logging options that are available on YARN.
For YARN applications, there are various logging options to choose from based on the
Data Fabric version and the types of applications that you
run. In 4.0.2 and later versions, you have the following logging options:
- For MapReduce version 2 (MRv2) applications, the default logging option is to log files on the local file system. However, central logging and YARN log aggregation are also available.
- For non-MapReduce applications, the default logging option is to log files on the local file system. However,YARN log aggregation is also available.
- Centralized Logging for MRv2
- Centralized logging provides an application-centric view of all the log files
generated by NodeManager nodes throughout the cluster. It enables users to gain a
complete picture of application execution by having all the logs available in a single
directory, without having to navigate from node to node.
The MapReduce program generates three types of log output:
- Standard output stream: captured in the
stdout
file - Standard error stream: captured in the
stderr
file - Log4j logs: captured in the
syslog
file
Centralized logs are available cluster-wide as they are written to the following local volume on the Data Fabric file system:var/mapr/local/<NodeManager node>/logs/yarn/userlogs
Since the log files are stored in a local volume directory that is associated with each NodeManager node, you run the
maprcli job linklogs
command to create symbolic links for all the logs in a single directory. You can then use tools such asgrep
andawk
to analyze them from an NFS mount point. You can also view the entire set of logs for a particular application using the HistoryServer UI. - Standard output stream: captured in the
- YARN Log Aggregation
- The YARN log aggregation option aggregates logs from the local file system and moves
log files for completed applications from the local file system to the Data Fabric file system. This allows users to view the entire
set of logs for a particular application using the HistoryServer UI or by running the
yarn logs
command.