Nexus configuration

Nexus Delta service can be highly customized using configuration file(s). Many things can be adapted to your deployment needs: port where the service is running, timeouts, the database you decide to support, pagination defaults, etc.

There are 3 ways to modify the default configuration:

• Setting the env variable DELTA_EXTERNAL_CONF which defines the path to a HOCON file. The configuration keys that are defined here can be overriden by the other methods.
• Using JVM properties as arguments when running the service: -D{property}. For example: -Dapp.http.interface="127.0.0.1".
• Using FORCE_CONFIG_{property} environment variables. In order to enable this style of configuration, the JVM property -Dconfig.override_with_env_vars=true needs to be set. Once set, a configuration flag can be overridden. For example: CONFIG_FORCE_app_http_interface="127.0.0.1".

In terms of JVM pool memory allocation, we recommend setting the following values to the JAVA_OPTSenvironment variable: -Xms4g -Xmx4g. The recommended values should be changed accordingly with the usage of Nexus Delta, the nomber of projects and the resources/schemas size.

In order to successfully run Nexus Delta there is a minimum set of configuration flags that need to be specified

Http configuration

This section of the configuration defines the binding address and port where the service will be listening.

The configuration flag akka.http.server.parsing.max-content-length can be used to control the maximum payload size allowed for Nexus Delta resources. This value applies to all posted resources except for files.

Database configuration

Since 1.5.0 Nexus Delta comes in two database flavours: postgres or cassandra. The configuration flag app.database.flavour is used to select the flavour.

Cassandra configuration

This section of the configuration defines the cassandra specific configuration (username, password, contact points, etc).

Before running Nexus Delta, the keyspace defined on the configuration app.database.cassandra.keyspace must be present along with the expected tables. However, one can let Nexus Delta automatically create keyspaces and tables using the following configuration parameters: app.database.cassandra.keyspace-autocreate=true and app.database.cassandra.tables-autocreate=true.

There are many other configuration parameters to customize the behaviour of the cassandra driver (timeouts, intervals, etc). These can be be found in the application-cassandra.conf file. One of the most relevant among these settings is: akka.persistence.cassandra.events-by-tag.first-time-bucket. Its value must be the date-time of the first event stored in Nexus Delta in the format YYYYMMDDTHH:MM.

Postgres configuration

This section of the configuration defines the postgres specific configuration (username, password, host, etc).

Before running Nexus Delta, the expected tables should be created. However, one can let Nexus Delta automatically them using the following configuration parameters: app.database.postgres.tables-autocreate=true

RDF parser

The underlying Apache Jena parser used to validate incoming data is now configurable to enable different levels of strictness.

Service account configuration

Nexus Delta uses a service account to perform automatic tasks under the hood. Examples of it are:

• Granting default ACLs to the user creating a project.
• Creating default views on project creation.

This section of the configuration defines the service account configuration.

Automatic project provisioning

Automatic project provisioning allows to create a dedicated project for users the first time they connect to Delta that is to say the first time, they query the project listing endpoints.

The generated project label will be:

• The current username where only non-diacritic alphabetic characters ([a-zA-Z]), numbers, dashes and underscores will be preserved
• This resulting string is then truncated to 64 characters if needed.

This feature can be turned on via the flag app.projects.automatic-provisioning.enabled.

This section of the configuration defines the project provisioning configuration.

Encryption configuration

Nexus Delta uses symmetric encryption to secure sensitive data information (tokens and passwords).

This section of the configuration defines the encryption configuration.

Plugins configuration

Since 1.5.0, Nexus Delta supports plugins. Jar files present inside the local directory defined by the DELTA_PLUGINS environment variable are loaded as plugins into the Delta service.

Each plugin configuration is rooted under plugins.{plugin_name}. All plugins have a plugins.{plugin_name}.priority configuration flag used to determine the order in which the routes are handled in case of collisions.

Elasticsearch views plugin configuration

The elasticsearch plugin configuration can be found here.

The most important flag are: * plugins.elasticsearch.base which defines the endpoint where the Elasticsearch service is running. * plugins.elasticsearch.credentials.username and plugins.elasticsearch.credentials.password to allow to access to a secured Elasticsearch cluster. The user provided should have the privileges to create/delete indices and read/index from them.

Please refer to the Elasticsearch configuration which describes the different steps to achieve this.

Blazegraph views plugin configuration

The blazegraph plugin configuration can be found here.

The most important flag is plugins.blazegraph.base which defines the endpoint where the Blazegraph service is running.

Composite views plugin configuration

The composite views plugin configuration can be found here.

There are several configuration flags related to tweaking the range of values allowed for sources, projections and rebuild interval.

Storage plugin configuration

The storage plugin configuration can be found here.

Nexus Delta supports 3 types of storages: ‘disk’, ‘amazon’ (s3 compatible) and ‘remote’.

• For disk storages the most relevant configuration flag is plugins.storage.storages.disk.default-volume, which defines the default location in the Nexus Delta filesystem where the files using that storage are going to be saved.
• For S3 compatible storages the most relevant configuration flags are the ones related to the S3 settings: plugins.storage.storages.amazon.default-endpoint, plugins.storage.storages.amazon.default-access-key and plugins.storage.storages.amazon.default-secret-key.
• For remote disk storages the most relevant configuration flags are plugins.storage.storages.remote-disk.default-endpoint (the endpoint where the remote storage service is running) and plugins.storage.storages.remote-disk.default-credentials (the Bearer token to authenticate to the remote storage service).

Archive plugin configuration

The archive plugin configuration can be found here.

Monitoring

For monitoring, Nexus Delta relies on Kamon.

Kamon can be disabled by passing the environment variable KAMON_ENABLED to false

Delta configuration for Kamon is provided here. For a more complete description on the different options available, please look at the Kamon website.

Instrumentation

Delta provides the Kamon instrumentation for:

• JDBC (only useful if you run Delta with PostgreSQL)
• Executors
• Scala futures
• Logback
• System metrics

Reporters

Kamon reporters are also available for:

• Jaeger
• Prometheus