Druid uses a module system that allows for the addition of extensions at runtime. Core extensions are bundled with the Druid tarball. Community extensions be download locally via the pull-deps tool.
Core Druid extensions are already bundled in the Druid release tarball. You can get them by downloading the tarball at druid.io.
Unpack the tarball; You will see an
extensions folder that contains all the core extensions, along with a
where it contains all the hadoop extensions. Each extension will have its own folder that contains extension jars. However, because of licensing
we didn't package the mysql-metadata-storage extension in the extensions folder. In order to get it, you can download it from druid.io,
then unpack and move it into
Optionally, you can use the
pull-deps tool to download extensions you want.
See pull-deps for a complete example.
There are two ways to let Druid load extensions.
If you add your extension jar to the classpath at runtime, Druid will load it into the system. This mechanism is relatively easy to reason about, but it also means that you have to ensure that all dependency jars on the classpath are compatible. That is, Druid makes no provisions while using this method to maintain class loader isolation so you must make sure that the jars on your classpath are mutually compatible.
If you don't want to fiddle with classpath, you can tell Druid to load extensions from an extension directory.
To let Druid load your extensions, follow the steps below
Tell Druid where your extensions are
druid.extensions.directory (the root directory that contains Druid extensions). See Configuration
The value for this property should be set to the absolute path of the folder that contains all the extensions.
In general, you should simply reuse the release tarball's extensions directory (i.e.,
Suppose you specify
extensions, it should look like this,
extensions/ ├── druid-kafka-eight │ ├── druid-kafka-eight-0.7.3.jar │ ├── jline-0.9.94.jar │ ├── jopt-simple-3.2.jar │ ├── kafka-clients-0.8.2.1.jar │ ├── kafka_2.10-0.8.2.1.jar │ ├── log4j-1.2.16.jar │ ├── lz4-1.3.0.jar │ ├── metrics-core-2.2.0.jar │ ├── netty-3.7.0.Final.jar │ ├── scala-library-2.10.4.jar │ ├── slf4j-log4j12-1.6.1.jar │ ├── snappy-java-126.96.36.199.jar │ ├── zkclient-0.3.jar └── mysql-metadata-storage ├── mysql-connector-java-5.1.34.jar └── mysql-metadata-storage-0.9.0.jar
As you can see, underneath
extensions there are two sub-directories
Each sub-directory denotes an extension that Druid could load.
Tell Druid what extensions to load
druid.extensions.loadList(See Configuration ) to specify a
list of names of extensions that should be loaded by Druid.
druid.extensions.loadList=["druid-kafka-eight", "mysql-metadata-storage"] instructs Druid to load
mysql-metdata-storage extensions. That is, the name you specified in the list should be the same as its extension folder's name.
If you specify
druid.extensions.loadList=, Druid won't load any extensions from the file system.
If you don't specify
druid.extensions.loadList, Druid will load all the extensions under the directory specified by