druid/docs/development/extensions.md

---
id: extensions
title: "Extensions"
---

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Druid implements an extension system that allows for adding functionality at runtime. Extensions
are commonly used to add support for deep storages (like HDFS and S3), metadata stores (like MySQL
and PostgreSQL), new aggregators, new input formats, and so on.

Production clusters will generally use at least two extensions; one for deep storage and one for a
metadata store. Many clusters will also use additional extensions.

## Core extensions

Core extensions are maintained by Druid committers.

|Name|Description|Docs|
|----|-----------|----|
|druid-avro-extensions|Support for data in Apache Avro data format.|[link](../development/extensions-core/avro.md)|
|druid-basic-security|Support for Basic HTTP authentication and role-based access control.|[link](../development/extensions-core/druid-basic-security.md)|
|druid-bloom-filter|Support for providing Bloom filters in druid queries.|[link](../development/extensions-core/bloom-filter.md)|
|druid-caffeine-cache|A local cache implementation backed by Caffeine.|[link](../configuration/index.html#cache-configuration)|
|druid-datasketches|Support for approximate counts and set operations with [DataSketches](https://datasketches.github.io/).|[link](../development/extensions-core/datasketches-extension.html)|
|druid-hdfs-storage|HDFS deep storage.|[link](../development/extensions-core/hdfs.html)|
|druid-histogram|Approximate histograms and quantiles aggregator. Deprecated, please use the [DataSketches quantiles aggregator](../development/extensions-core/datasketches-quantiles.html) from the `druid-datasketches` extension instead.|[link](../development/extensions-core/approximate-histograms.html)|
|druid-kafka-extraction-namespace|Kafka-based namespaced lookup. Requires namespace lookup extension.|[link](../development/extensions-core/kafka-extraction-namespace.html)|
|druid-kafka-indexing-service|Supervised exactly-once Kafka ingestion for the indexing service.|[link](../development/extensions-core/kafka-ingestion.html)|
|druid-kinesis-indexing-service|Supervised exactly-once Kinesis ingestion for the indexing service.|[link](../development/extensions-core/kinesis-ingestion.html)|
|druid-kerberos|Kerberos authentication for druid processes.|[link](../development/extensions-core/druid-kerberos.html)|
|druid-lookups-cached-global|A module for [lookups](../querying/lookups.html) providing a jvm-global eager caching for lookups. It provides JDBC and URI implementations for fetching lookup data.|[link](../development/extensions-core/lookups-cached-global.html)|
|druid-lookups-cached-single| Per lookup caching module to support the use cases where a lookup need to be isolated from the global pool of lookups |[link](../development/extensions-core/druid-lookups.html)|
|druid-orc-extensions|Support for data in Apache Orc data format.|[link](../development/extensions-core/orc.html)|
|druid-parquet-extensions|Support for data in Apache Parquet data format. Requires druid-avro-extensions to be loaded.|[link](../development/extensions-core/parquet.html)|
|druid-protobuf-extensions| Support for data in Protobuf data format.|[link](../development/extensions-core/protobuf.html)|
|druid-s3-extensions|Interfacing with data in AWS S3, and using S3 as deep storage.|[link](../development/extensions-core/s3.html)|
|druid-ec2-extensions|Interfacing with AWS EC2 for autoscaling middle managers|UNDOCUMENTED|
|druid-stats|Statistics related module including variance and standard deviation.|[link](../development/extensions-core/stats.md)|
|mysql-metadata-storage|MySQL metadata store.|[link](../development/extensions-core/mysql.md)|
|postgresql-metadata-storage|PostgreSQL metadata store.|[link](../development/extensions-core/postgresql.md)|
|simple-client-sslcontext|Simple SSLContext provider module to be used by Druid's internal HttpClient when talking to other Druid processes over HTTPS.|[link](../development/extensions-core/simple-client-sslcontext.md)|

## Community extensions

> Community extensions are not maintained by Druid committers, although we accept patches from community members using these extensions. They may not have been as extensively tested as the core extensions.

A number of community members have contributed their own extensions to Druid that are not packaged with the default Druid tarball.
If you'd like to take on maintenance for a community extension, please post on [dev@druid.apache.org](https://lists.apache.org/list.html?dev@druid.apache.org) to let us know!

All of these community extensions can be downloaded using [pull-deps](../operations/pull-deps.html) while specifying a `-c` coordinate option to pull `org.apache.druid.extensions.contrib:{EXTENSION_NAME}:{DRUID_VERSION}`.

|Name|Description|Docs|
|----|-----------|----|
|ambari-metrics-emitter|Ambari Metrics Emitter |[link](../development/extensions-contrib/ambari-metrics-emitter.html)|
|druid-azure-extensions|Microsoft Azure deep storage.|[link](../development/extensions-contrib/azure.html)|
|druid-cassandra-storage|Apache Cassandra deep storage.|[link](../development/extensions-contrib/cassandra.html)|
|druid-cloudfiles-extensions|Rackspace Cloudfiles deep storage and firehose.|[link](../development/extensions-contrib/cloudfiles.html)|
|druid-distinctcount|DistinctCount aggregator|[link](../development/extensions-contrib/distinctcount.html)|
|druid-redis-cache|A cache implementation for Druid based on Redis.|[link](../development/extensions-contrib/redis-cache.html)|
|druid-time-min-max|Min/Max aggregator for timestamp.|[link](../development/extensions-contrib/time-min-max.html)|
|druid-google-extensions|Google Cloud Storage deep storage.|[link](../development/extensions-contrib/google.html)|
|sqlserver-metadata-storage|Microsoft SqlServer deep storage.|[link](../development/extensions-contrib/sqlserver.html)|
|graphite-emitter|Graphite metrics emitter|[link](../development/extensions-contrib/graphite.html)|
|statsd-emitter|StatsD metrics emitter|[link](../development/extensions-contrib/statsd.html)|
|kafka-emitter|Kafka metrics emitter|[link](../development/extensions-contrib/kafka-emitter.html)|
|druid-thrift-extensions|Support thrift ingestion |[link](../development/extensions-contrib/thrift.html)|
|druid-opentsdb-emitter|OpenTSDB metrics emitter |[link](../development/extensions-contrib/opentsdb-emitter.html)|
|materialized-view-selection, materialized-view-maintenance|Materialized View|[link](../development/extensions-contrib/materialized-view.html)|
|druid-moving-average-query|Support for [Moving Average](https://en.wikipedia.org/wiki/Moving_average) and other Aggregate [Window Functions](https://en.wikibooks.org/wiki/Structured_Query_Language/Window_functions) in Druid queries.|[link](../development/extensions-contrib/moving-average-query.html)|
|druid-influxdb-emitter|InfluxDB metrics emitter|[link](../development/extensions-contrib/influxdb-emitter.html)|
|druid-momentsketch|Support for approximate quantile queries using the [momentsketch](https://github.com/stanford-futuredata/momentsketch) library|[link](../development/extensions-contrib/momentsketch-quantiles.html)|
|druid-tdigestsketch|Support for approximate sketch aggregators based on [T-Digest](https://github.com/tdunning/t-digest)|[link](../development/extensions-contrib/tdigestsketch-quantiles.html)|

## Promoting community extensions to core extensions

Please post on [dev@druid.apache.org](https://lists.apache.org/list.html?dev@druid.apache.org) if you'd like an extension to be promoted to core.
If we see a community extension actively supported by the community, we can promote it to core based on community feedback.


For information how to create your own extension, please see [here](../development/modules.md).

## Loading extensions

### Loading core extensions

Apache Druid (incubating) bundles all [core extensions](../development/extensions.html#core-extensions) out of the box.
See the [list of extensions](../development/extensions.html#core-extensions) for your options. You
can load bundled extensions by adding their names to your common.runtime.properties
`druid.extensions.loadList` property. For example, to load the *postgresql-metadata-storage* and
*druid-hdfs-storage* extensions, use the configuration:

```
druid.extensions.loadList=["postgresql-metadata-storage", "druid-hdfs-storage"]
```

These extensions are located in the `extensions` directory of the distribution.

> Druid bundles two sets of configurations: one for the [quickstart](../tutorials/index.md) and
> one for a [clustered configuration](../tutorials/cluster.md). Make sure you are updating the correct
> common.runtime.properties for your setup.

> Because of licensing, the mysql-metadata-storage extension does not include the required MySQL JDBC driver. For instructions
> on how to install this library, see the [MySQL extension page](../development/extensions-core/mysql.md).

### Loading community extensions

You can also load community and third-party extensions not already bundled with Druid. To do this, first download the extension and
then install it into your `extensions` directory. You can download extensions from their distributors directly, or
if they are available from Maven, the included [pull-deps](../operations/pull-deps.md) can download them for you. To use *pull-deps*,
specify the full Maven coordinate of the extension in the form `groupId:artifactId:version`. For example,
for the (hypothetical) extension *com.example:druid-example-extension:1.0.0*, run:

```
java \
  -cp "lib/*" \
  -Ddruid.extensions.directory="extensions" \
  -Ddruid.extensions.hadoopDependenciesDir="hadoop-dependencies" \
  org.apache.druid.cli.Main tools pull-deps \
  --no-default-hadoop \
  -c "com.example:druid-example-extension:1.0.0"
```

You only have to install the extension once. Then, add `"druid-example-extension"` to
`druid.extensions.loadList` in common.runtime.properties to instruct Druid to load the extension.

> Please make sure all the Extensions related configuration properties listed [here](../configuration/index.md#extensions) are set correctly.

> The Maven groupId for almost every [community extension](../development/extensions.md#community-extensions) is org.apache.druid.extensions.contrib. The artifactId is the name
> of the extension, and the version is the latest Druid stable version.

### Loading extensions from the classpath

If you add your extension jar to the classpath at runtime, Druid will also 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.