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Elasticsearch

Elasticsearch is a distributed, RESTful search and analytics engine capable of solving a growing number of use cases. As the heart of the Elastic Stack, it centrally stores your data so you can discover the expected and uncover the unexpected.

— Elasticsearch Overview

JanusGraph supports Elasticsearch as an index backend. Here are some of the Elasticsearch features supported by JanusGraph:

  • Full-Text: Supports all Text predicates to search for text properties that matches a given word, prefix or regular expression.
  • Geo: Supports all Geo predicates to search for geo properties that are intersecting, within, disjoint to or contained in a given query geometry. Supports points, circles, boxes, lines and polygons for indexing. Supports circles, boxes and polygons for querying point properties and all shapes for querying non-point properties.
  • Numeric Range: Supports all numeric comparisons in Compare.
  • Flexible Configuration: Supports remote operation and open-ended settings customization.
  • Collections: Supports indexing SET and LIST cardinality properties.
  • Temporal: Nanosecond granularity temporal indexing.
  • Custom Analyzer: Choose to use a custom analyzer

Please see Version Compatibility for details on what versions of Elasticsearch will work with JanusGraph.

Important

JanusGraph uses sandboxed https://www.elastic.co/guide/en/elasticsearch/reference/master/modules-scripting-painless.html[Painless scripts] for inline updates, which are enabled by default in Elasticsearch.

Running Elasticsearch

JanusGraph supports connections to a running Elasticsearch cluster. JanusGraph provides two options for running local Elasticsearch instances for getting started quickly. JanusGraph server (see Getting started) automatically starts a local Elasticsearch instance. Alternatively JanusGraph releases include a full Elasticsearch distribution to allow users to manually start a local Elasticsearch instance (see this page for more information).

$ elasticsearch/bin/elasticsearch

Note

For security reasons Elasticsearch must be run under a non-root account

Elasticsearch Configuration Overview

JanusGraph supports HTTP(S) client connections to a running Elasticsearch cluster. Please see Version Compatibility for details on what versions of Elasticsearch will work with the different client types in JanusGraph.

Note

JanusGraph’s index options start with the string "index.[X]." where "[X]" is a user-defined name for the backend. This user-defined name must be passed to JanusGraph’s ManagementSystem interface when building a mixed index, as described in Mixed Index, so that JanusGraph knows which of potentially multiple configured index backends to use. Configuration snippets in this chapter use the name search, whereas prose discussion of options typically write [X] in the same position. The exact index name is not significant as long as it is used consistently in JanusGraph’s configuration and when administering indices.

Tip

It’s recommended that index names contain only alphanumeric lowercase characters and hyphens, and that they start with a lowercase letter.

Connecting to Elasticsearch

The Elasticsearch client is specified as follows: 

index.search.backend=elasticsearch

When connecting to Elasticsearch a single or list of hostnames for the Elasticsearch instances must be provided. These are supplied via JanusGraph’s index.[X].hostname key. 

index.search.backend=elasticsearch
index.search.hostname=10.0.0.10:9200

Each host or host:port pair specified here will be added to the HTTP client’s round-robin list of request targets. Here’s a minimal configuration that will round-robin over 10.0.0.10 on the default Elasticsearch HTTP port (9200) and 10.0.0.20 on port 7777: 

index.search.backend=elasticsearch
index.search.hostname=10.0.0.10, 10.0.0.20:7777

JanusGraph index.[X] and index.[X].elasticsearch options

JanusGraph only uses default values for index-name and health-request-timeout. See Configuration Reference for descriptions of these options and their accepted values.

  • index.[X].index-name
  • index.[X].elasticsearch.health-request-timeout

REST Client Options

The REST client accepts the index.[X].bulk-refresh option. This option controls when changes are made visible to search. See ?refresh documentation for more information.

REST Client HTTPS Configuration

SSL support for HTTP can be enabled by setting the index.[X].elasticsearch.ssl.enabled configuration option to true. Note that depending on your configuration you may need to change the value of index.[X].port if your HTTPS port number is different from the default one for the REST API (9200).

When SSL is enabled you may also configure the location and password of the truststore. This can be done as follows:

index.search.elasticsearch.ssl.truststore.location=/path/to/your/truststore.jks
index.search.elasticsearch.ssl.truststore.password=truststorepwd

Note that these settings apply only to Elasticsearch REST client and do not affect any other SSL connections in JanusGraph.

Configuration of the client keystore is also supported:

index.search.elasticsearch.ssl.keystore.location=/path/to/your/keystore.jks
index.search.elasticsearch.ssl.keystore.storepassword=keystorepwd
index.search.elasticsearch.ssl.keystore.keypassword=keypwd

Any of the passwords can be empty.

If needed, the SSL hostname verification can be disabled by setting the index.[X].elasticsearch.ssl.disable-hostname-verification property value to true and the support for self-signed SSL certificates can be enabled by setting index.[X].elasticsearch.ssl.allow-self-signed-certificates property value to true.

Tip

It is not recommended to rely on the self-signed SSL certificates or to disable the hostname verification for a production system as it significantly limits the client's ability to provide the secure communication channel with the Elasticsearch server(s). This may result in leaking the confidential data which may be a part of your JanusGraph index.

REST Client HTTP Authentication

REST client supports the following authentication options: Basic HTTP Authentication (username/password) and custom authentication based on the user-provided implementation.

These authentication methods are independent from SSL client authentication described above.

REST Client Basic HTTP Authentication

Basic HTTP Authentication is available regardless of the state of SSL support. Optionally, an authentication realm can be specified via index.[X].elasticsearch.http.auth.basic.realm property.

index.search.elasticsearch.http.auth.type=basic
index.search.elasticsearch.http.auth.basic.username=httpuser
index.search.elasticsearch.http.auth.basic.password=httppassword

Tip

It is highly recommended to use SSL (e.g. setting index.[X].elasticsearch.ssl.enabled to true) when using this option as the credentials can be intercepted when sent over an unencrypted connection!

REST Client Custom HTTP Authentication

Additional authentication methods can be implemented by providing your own implementation. The custom authenticator is configured as follows:

index.search.elasticsearch.http.auth.type=custom
index.search.elasticsearch.http.auth.custom.authenticator-class=fully.qualified.class.Name
index.search.elasticsearch.http.auth.custom.authenticator-args=arg1,arg2,...

Argument list is optional and can be empty.

The class specified there has to implement the org.janusgraph.diskstorage.es.rest.util.RestClientAuthenticator interface or extend org.janusgraph.diskstorage.es.rest.util.RestClientAuthenticatorBase convenience class. The implementation gets access to HTTP client configuration and can customize the client as needed. Refer to <> for more information.

For example, the following code snippet implements an authenticator allowing the Elasticsearch REST client to authenticate and get authorized against AWS IAM:

import java.io.IOException;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import org.apache.http.HttpRequestInterceptor;
import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
import org.janusgraph.diskstorage.es.rest.util.RestClientAuthenticatorBase;
import com.amazonaws.auth.DefaultAWSCredentialsProviderChain;
import com.amazonaws.regions.DefaultAwsRegionProviderChain;
import com.google.common.base.Supplier;
import vc.inreach.aws.request.AWSSigner;
import vc.inreach.aws.request.AWSSigningRequestInterceptor;
/**
 * <p>
 * Elasticsearch REST HTTP(S) client callback implementing AWS request signing.
 * </p>
 * <p>
 * The signer is based on AWS SDK default provider chain, allowing multiple options for providing
 * the caller credentials. See {@link DefaultAWSCredentialsProviderChain} documentation for the details.
 * </p>
 */
public class AWSV4AuthHttpClientConfigCallback extends RestClientAuthenticatorBase {
    private static final String AWS_SERVICE_NAME = "es";
    private HttpRequestInterceptor awsSigningInterceptor;
    public AWSV4AuthHttpClientConfigCallback(final String[] args) {
        // does not require any configuration
    }
    @Override
    public void init() throws IOException {
        DefaultAWSCredentialsProviderChain awsCredentialsProvider = new DefaultAWSCredentialsProviderChain();
        final Supplier<LocalDateTime> clock = () -> LocalDateTime.now(ZoneOffset.UTC);
        // using default region provider chain
        // (https://docs.aws.amazon.com/sdk-for-java/v2/developer-guide/java-dg-region-selection.html)
        DefaultAwsRegionProviderChain regionProviderChain = new DefaultAwsRegionProviderChain();
        final String awsRegion = regionProviderChain.getRegion();
        final AWSSigner awsSigner = new AWSSigner(awsCredentialsProvider, awsRegion, AWS_SERVICE_NAME, clock);
        this.awsSigningInterceptor = new AWSSigningRequestInterceptor(awsSigner);
    }
    @Override
    public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) {
        return httpClientBuilder.addInterceptorLast(awsSigningInterceptor);/
    }
}

This custom authenticator does not use any constructor arguments.

Ingest Pipelines

Different ingest pipelines can be set for each mixed index. Ingest pipeline can be use to pre-process documents before indexing. A pipeline is composed by a series of processors. Each processor transforms the document in some way. For example date processor can extract a date from a text to a date field. So you can query this date with JanusGraph without it being physically in the primary storage.

  • index.[X].elasticsearch.ingest-pipeline.[mixedIndexName] = pipeline_id

See ingest documentation for more information about ingest pipelines and processors documentation for more information about ingest processors.

Secure Elasticsearch

Elasticsearch does not perform authentication or authorization. A client that can connect to Elasticsearch is trusted by Elasticsearch. When Elasticsearch runs on an unsecured or public network, particularly the Internet, it should be deployed with some type of external security. This is generally done with a combination of firewalling, tunneling of Elasticsearch’s ports or by using Elasticsearch extensions such as X-Pack. Elasticsearch has two client-facing ports to consider:

  • The HTTP REST API, usually on port 9200
  • The native "transport" protocol, usually on port 9300

A client uses either one protocol/port or the other, but not both simultaneously. Securing the HTTP protocol port is generally done with a combination of firewalling and a reverse proxy with SSL encryption and HTTP authentication. There are a couple of ways to approach security on the native "transport" protocol port:

In addition to that, some hosted Elasticsearch services offer other methods of authentication and authorization. For example, AWS Elasticsearch Service requires the use of HTTPS and offers an option for using IAM-based access control. For that the requests sent to this service must be signed. This can be achieved by using a custom authenticator (see above).

Tunnel Elasticsearch's native "transport" protocol:: This approach can be implemented with SSL/TLS tunneling (for instance via stunnel), a VPN, or SSH port forwarding. SSL/TLS tunnels require non-trivial setup and monitoring: one or both ends of the tunnel need a certificate, and the stunnel processes need to be configured and running continuously. The setup for most secure VPNs is likewise non-trivial. Some Elasticsearch service providers handle server-side tunnel management and provide a custom Elasticsearch transport.type to simplify the client setup.

Add a firewall rule that allows only trusted clients to connect on Elasticsearch’s native protocol port
This is typically done at the host firewall level. Easy to configure, but very weak security by itself.

Index Creation Options

JanusGraph supports customization of the index settings it uses when creating its Elasticsearch index. It allows setting arbitrary key-value pairs on the settings object in the Elasticsearch create index request issued by JanusGraph. Here is a non-exhaustive sample of Elasticsearch index settings that can be customized using this mechanism:

  • index.number_of_replicas
  • index.number_of_shards
  • index.refresh_interval

Settings customized through this mechanism are only applied when JanusGraph attempts to create its index in Elasticsearch. If JanusGraph finds that its index already exists, then it does not attempt to recreate it, and these settings have no effect.

Embedding Elasticsearch index creation settings with create.ext

JanusGraph iterates over all properties prefixed with index.[X].elasticsearch.create.ext., where [X] is an index name such as search. It strips the prefix from each property key. The remainder of the stripped key will be interpreted as an Elasticsearch index creation setting. The value associated with the key is not modified. The stripped key and unmodified value are passed as part of the settings object in the Elasticsearch create index request that JanusGraph issues when bootstrapping on Elasticsearch. This allows embedding arbitrary index creation settings settings in JanusGraph’s properties. Here’s an example configuration fragment that customizes three Elasticsearch index settings using the create.ext config mechanism:

index.search.backend=elasticsearch
index.search.elasticsearch.create.ext.number_of_shards=15
index.search.elasticsearch.create.ext.number_of_replicas=3
index.search.elasticsearch.create.ext.shard.check_on_startup=true

The configuration fragment listed above takes advantage of Elasticsearch’s assumption, implemented server-side, that unqualified create index setting keys have an index. prefix. It’s also possible to spell out the index prefix explicitly. Here’s a JanusGraph config file functionally equivalent to the one listed above, except that the index. prefix before the index creation settings is explicit: 

index.search.backend=elasticsearch
index.search.elasticsearch.create.ext.index.number_of_shards=15
index.search.elasticsearch.create.ext.index.number_of_replicas=3
index.search.elasticsearch.create.ext.index.shard.check_on_startup=false

Tip

The create.ext mechanism for specifying index creation settings is compatible with JanusGraph’s Elasticsearch configuration.

Troubleshooting

Connection Issues to remote Elasticsearch cluster

Check that the Elasticsearch cluster nodes are reachable on the HTTP protocol port from the JanusGraph nodes. Check the node listen port by examining the Elasticsearch node configuration logs or using a general diagnostic utility like netstat. Check the JanusGraph configuration.

Optimizing Elasticsearch

Write Optimization

For bulk loading or other write-intense applications, consider increasing Elasticsearch’s refresh interval. Refer to this discussion on how to increase the refresh interval and its impact on write performance. Note, that a higher refresh interval means that it takes a longer time for graph mutations to be available in the index.

Further Reading

  • Please refer to the Elasticsearch homepage and available documentation for more information on Elasticsearch and how to setup an Elasticsearch cluster.