Working with DataHub

Cumulocity DataHub Edge overview

Documentation overview

The following sections will walk you through all the functionalities of Cumulocity DataHub Edge in detail.

For your convenience, here is an overview of the contents:

Cumulocity DataHub Edge at a glance

Cumulocity Edge is an onsite, single-server, and single-tenant variant of the Cumulocity Core platform. It is delivered as a software appliance designed to run on industrial PCs or local servers. Cumulocity DataHub is available as an add-on to Cumulocity Edge.

Cumulocity DataHub Edge offers the same functionality as the cloud-variant of Cumulocity DataHub, but stores the data locally. You can define offloading pipelines, which regularly move data from the Operational Store of Cumulocity into a data lake. In the Edge setup, a NAS is used as data lake. Dremio, the internal engine of Cumulocity DataHub, can access the data lake and run analytical queries against its contents, using SQL as the query interface.

Cumulocity DataHub Edge consists of the following building blocks:

• The Cumulocity DataHub UI is deployed as a web application in the Cumulocity core. It provides the frontend for defining and managing offloading pipelines.
• The Cumulocity DataHub backend manages offloading pipelines and their scheduled execution. The backend and its associated database run within one Docker container in the Docker daemon. Its internal state, for example, the defined offloading configurations, is persisted on the central data disk.
• The query processing is based on a Dremio master and a Dremio executor as well as on a ZooKeeper instance. Dremio master and ZooKeeper run in one Docker container and the Dremio executor runs in another one. Both containers are run by the Docker daemon. The internal state of the containers, for example, the query job history, is persisted on the central data disk. In the above figure just Dremio is shown for reasons of simplicity.
• The data lake is located on the central data disk.

Cumulocity DataHub Edge versus Cumulocity DataHub cloud deployments

Cumulocity DataHub Edge uses the same software as Cumulocity DataHub, though in the following aspects these two variants differ:

Setting up Cumulocity DataHub Edge

Prerequisites

Before setting up Cumulocity DataHub Edge, you must check the following prerequisites:

Hardware requirements

The hardware requirements for running a bare Cumulocity Edge instance are described in Requirements. When Cumulocity DataHub Edge is additionally running, the hardware requirements of the virtual machine are as follows:

• 100 GB of free disk space plus sufficient free disk space for the data lake contents
• Intel x86 CPU
• Recommended: 12 GB RAM, minimum: 8 GB RAM
• Recommended: 4 logical CPU cores, minimum: 2 logical CPU cores
• One NIC

Hardware requirements for the host OS are excluded.

Setting up Cumulocity DataHub Edge

Copy the Cumulocity DataHub Edge archive to the Cumulocity Edge.

scp datahub-edge.tar admin@<edge_ip_address>:/tmp

Log in as admin into Cumulocity Edge.

ssh admin@<edge_ip_address>

Run the install script.

sudo /opt/c8y/utilities/install_signed_package.sh /tmp/datahub-edge.tar

During script execution, you are prompted for the username and password of the administration user of the tenant edge. During installation, you are also prompted to set the new password of the Dremio admin account. It takes a few minutes to complete the installation. After completion you can delete the Cumulocity DataHub Edge archive.

The install script runs the following basic steps:

• Deploy the Cumulocity DataHub Edge UI as a web application to Cumulocity Core
• Start a Docker container with the Cumulocity DataHub Edge backend and the database system for managing the backend state
• Start a Docker container with the Dremio master and a ZooKeeper instance
• Start a Docker container with the Dremio executor
• Configure corresponding roles and permissions in Cumulocity Core

The Docker containers will be restarted automatically if the container itself fails or the applications within are no longer reachable.

The containers are configured to store their application state on the data disk under /opt/mongodb:

• /cdh-master/data: the state of the Dremio master
• /cdh-executor/data: the state of the Dremio executor
• /cdh-console/db: the state of the Cumulocity DataHub Edge backend
• /cdh-master/datalake: the data lake folder

Upgrading Cumulocity DataHub Edge

An upgrade of Cumulocity DataHub Edge follows the same steps as the initial setup. First, you must copy the archive with the new version to Cumulocity Edge. Next, you must log in as admin. Then you must run the install script using the new version.

sudo /opt/c8y/utilities/install_signed_package.sh /tmp/datahub-<NEW version>.tar

During script execution, the already installed version is detected and the script runs an upgrade using the new version. It takes a few minutes to complete the installation. After completion you can delete the Cumulocity DataHub Edge archive.

Adapting to network changes of Cumulocity Edge

There might be cases where you must change the network setup of your Edge installation, for example by setting the IP range used by Edge internally or changing the domain name. The network configuration of Cumulocity DataHub Edge must be adapted to such a change by running the script /opt/softwareag/cdh/bin/restart.sh once. The script restarts Cumulocity DataHub with parameters aligned with the new network configuration.

Accessing Cumulocity DataHub Edge

The different Cumulocity DataHub Edge interfaces can be accessed in the same way as in a cloud deployment of Cumulocity DataHub.

Defining Cumulocity DataHub permissions and roles

The definition and assignment of permissions and roles is done in the same way as in a cloud deployment. See Defining Cumulocity DataHub permissions and roles for details.

Setting up Dremio account and data lake

The setup of the Dremio account and the data lake is done in the same way as in a cloud deployment. See Setting up Cumulocity DataHub for details.

Cumulocity DataHub Edge is configured to use a NAS as data lake. When configuring the NAS use as mount path /datalake. This path is mounted to /opt/mongodb/cdh-master/datalake.

Changing Dremio memory configuration on Cumulocity DataHub Edge

Depending on the use case, it might be necessary to increase the memory available to Dremio, the internal engine of Cumulocity DataHub. By default, Dremio is configured to consume a maximum of 4 GB of RAM (2 GB assigned to both master node and executor node).

Depending on the situation, one either must increase the memory of Dremio’s master or executor node. In many cases, the master node’s memory is the limiting factor, but not always. Inspecting the query profiles in Dremio helps to determine where the bottleneck occurs.

Master node memory configuration

Run the following steps:

• Log into edge via SSH
• As root, run vi /etc/cdh/cdh-master/dremio-env and change DREMIO_MAX_HEAP_MEMORY_SIZE_MB=1750 and DREMIO_MAX_DIRECT_MEMORY_SIZE_MB=250 to your needs. For example, you can double both values.
• Run service cdh-master restart.

Executor node memory configuration

Run the following steps:

• Log into edge via SSH
• As root, run vi /etc/cdh/cdh-executor/dremio-env and change DREMIO_MAX_HEAP_MEMORY_SIZE_MB=1024 and DREMIO_MAX_DIRECT_MEMORY_SIZE_MB=1488 to your needs. For example, you can double both values.
• Run service cdh-executor restart.

Working with Cumulocity DataHub Edge

Cumulocity DataHub Edge offers the same set of functionality as the cloud variant. See Working with Cumulocity DataHub for details on configuring and monitoring offloading jobs, querying offloaded Cumulocity data, and refining offloaded Cumulocity data.

Operating Cumulocity DataHub Edge

Similar to the cloud variant, Cumulocity DataHub Edge UI allows you to check system information and view audit logs. See Operating Cumulocity DataHub for details.

When managing Cumulocity DataHub Edge, the following standard tasks are additionally relevant.

Troubleshooting the system

If problems occur, you should follow these steps:

• Perform a health check, see Health check
• Check the log files, see Log files
• Monitor the system processes, see Monitoring

If you need to contact product support, include the output of the diagnostics script. See Diagnostic utility for details of how to run it.

Health check

Check Cumulocity DataHub Edge backend status

You can check the status of the backend in the Administration page of the Cumulocity DataHub UI. Alternatively you can query the isalive endpoint, which should produce an output similar to:

curl --user admin:your_password https://edge_domain_name/service/datahub/isalive

{
  "timestamp" : 1582204706844,
  "version" : {
    "versionId" : "10.6.0.0.337",
    "build" : "202002200050",
    "scmRevision" : "4ddbb70bf96eb82a2f6c5e3f32c20ff206907f43"
  }
}

If the backend cannot be reached, you will get an error response.

Check Dremio backend status

You can check the status of Dremio using the server_status endpoint:

curl http://datahub.edge_domain_name/apiv2/server_status
"OK"

Dremio is running if OK is returned. No response will be returned if it is not running or inaccessible.

Log files

The installation log file is stored at /var/log/cdh.

In order to access the logs of the Cumulocity DataHub and Dremio containers, you must use the Docker logs command. To follow the logs of cdh-master you must run:

docker logs -f cdh-master

To follow the logs of cdh-executor you must run:

docker logs -f cdh-executor

The containers are configured to rotate log files with rotation settings of two days and a maximum file size of 10 MB.

Monitoring

Cumulocity Edge uses Monit for management and monitoring of relevant processes. See Monitoring for details. The Cumulocity DataHub Edge processes, namely the Cumulocity DataHub backend and the Dremio nodes, are also monitored by Monit.

Data disk management and monitoring

The data disk is used for storing the state of Cumulocity DataHub and Dremio and serves as data lake. In order to ensure that the system can work properly, the disk must not run out of space. The main factors for the disk space allocation of Cumulocity DataHub Edge are the Dremio job profiles and the data lake contents.

Cleanup of Dremio job history

Dremio maintains a history of job details and profiles, which can be inspected in Dremio’s job log, that is, the Jobs page of the Dremio UI. This job history must be cleaned up regularly to free the resources necessary for storing it.

Dremio is configured to perform the cleanup of job results automatically without downtime. The default value for the maximum age of stored job results is seven days. To change that value, a Dremio administrator must modify the support key jobs.max.age_in_days. The changes become effective within 24 hours or after restarting Dremio. See the corresponding Dremio documentation for more details on support keys.

Cleanup of data lake contents

The data lake contents are not automatically purged, as the main purpose of Cumulocity DataHub is to maintain a history of data. However, if disk space is critical and cannot be freed otherwise, parts of the data lake contents must be deleted. Instead of deleting you might also move the data.

Browse to the data lake folder /opt/mongodb/cdh-master/datalake and select the folder whose name equals the target table of the offloading pipeline. The data within the data lake is organized hierarchically, as described in section Folder structure. To free up disk space, delete the chunk folders and all monthly/daily folders up to a point in time fitting to your needs. For example, delete all folders whose filename indicates that the data is older than 1st of January 2024. In general, you must delete complete folders, not single files within a folder. After you delete the folders, you must make Dremio aware of the changed data lake contents. Given the path to your target table, run the following query in Dremio as an administrator:

ALTER PDS <target_table_path> REFRESH METADATA FORCE UPDATE

Backup and Restore

Cumulocity DataHub’s runtime state as well as the data lake containing offloaded data reside in the Cumulocity Edge server VM. In order to back up and restore Cumulocity DataHub, its runtime state, and its data we recommend you to back up and recover the Cumulocity Edge server VM as described in Backup and restore.