Features Overview ================= This page highlights some of the most prominent features available in sahara. The guidance provided here is primarily focused on the runtime aspects of sahara. For discussions about configuring the sahara server processes please see the :doc:`configuration.guide` and :doc:`advanced.configuration.guide`. Anti-affinity ------------- One of the problems with running data processing applications on OpenStack is the inability to control where an instance is actually running. It is not always possible to ensure that two new virtual machines are started on different physical machines. As a result, any replication within the cluster is not reliable because all replicas may be co-located on one physical machine. To remedy this, sahara provides the anti-affinity feature to explicitly command all instances of the specified processes to spawn on different Compute nodes. This is especially useful for Hadoop data node processes to increase HDFS replica reliability. Starting with the Juno release, sahara can create server groups with the ``anti-affinity`` policy to enable this feature. Sahara creates one server group per cluster and assigns all instances with affected processes to this server group. Refer to the `Nova documentation`_ on how server groups work. This feature is supported by all plugins out of the box, and can be enabled during the cluster template creation. .. _Nova documentation: http://docs.openstack.org/developer/nova Block Storage support --------------------- OpenStack Block Storage (cinder) can be used as an alternative for ephemeral drives on instances. Using Block Storage volumes increases the reliability of data which is important for HDFS services. A user can set how many volumes will be attached to each instance in a node group and the size of each volume. All volumes are attached during cluster creation and scaling operations. Cluster scaling --------------- Cluster scaling allows users to change the number of running instances in a cluster without needing to recreate the cluster. Users may increase or decrease the number of instances in node groups or add new node groups to existing clusters. If a cluster fails to scale properly, all changes will be rolled back. Data locality ------------- For optimal performance, it is best for data processing applications to work on data local to the same rack, OpenStack Compute node, or virtual machine. Hadoop supports a data locality feature and can schedule jobs to task tracker nodes that are local for the input stream. In this manner the task tracker nodes can communicate directly with the local data nodes. Sahara supports topology configuration for HDFS and Object Storage data sources. For more information on configuring this option please see the :ref:`data_locality_configuration` documentation. Volume-to-instance locality --------------------------- Having an instance and an attached volume on the same physical host can be very helpful in order to achieve high-performance disk I/O operations. To achieve this, sahara provides access to the Block Storage volume instance locality functionality. For more information on using volume instance locality with sahara, please see the :ref:`volume_instance_locality_configuration` documentation. Distributed Mode ---------------- The :doc:`installation.guide` suggests launching sahara as a single ``sahara-all`` process. It is also possible to run sahara in distributed mode with ``sahara-api`` and ``sahara-engine`` processes running on several machines simultaneously. Running in distributed mode allows sahara to offload intensive tasks to the engine processes while keeping the API process free to handle requests. For an expanded discussion of configuring sahara to run in distributed mode please see the :ref:`distributed-mode-configuration` documentation. Hadoop HDFS High Availability ----------------------------- Hadoop HDFS High Availability (HDFS HA) provides an architecture to ensure that HDFS will continue to work in the result of an active namenode failure. It uses 2 namenodes in an active/passive configuration to provide this availability. High availability is achieved by using a set of journalnodes. Zookeeper servers, and ZooKeeper Failover Controllers (ZKFC), as well as additional configuration changes to HDFS and other services that use HDFS. Currently HDFS HA is supported with the HDP 2.0.6 plugin and CDH 5.4.0 plugin. In HDP 2.0.6 plugin, the feature is enabled through a ``cluster_configs`` parameter in the cluster's JSON: .. sourcecode:: cfg "cluster_configs": { "HDFSHA": { "hdfs.nnha": true } } In CDH 5.4.0 plugin, the HDFS HA is enabled through adding several HDFS_JOURNALNODE roles in the node group templates of cluster template. When HDFS_JOURNALNODE roles are added and the roles setup meets below requirements, the HDFS HA is enabled. * HDFS_JOURNALNODE number is odd, and at least 3. * Zookeeper is enabled. * NameNode and SecondaryNameNode are on different physical hosts by setting anti-affinity. In this case, the original SecondrayNameNode node will be used as the Standby NameNode. Networking support ------------------ Sahara supports both the nova-network and neutron implementations of OpenStack Networking. By default sahara is configured to behave as if the nova-network implementation is available. For OpenStack installations that are using the neutron project please see :ref:`neutron-nova-network`. Object Storage support ---------------------- Sahara can use OpenStack Object Storage (swift) to store job binaries and data sources utilized by its job executions and clusters. In order to leverage this support within Hadoop, including using Object Storage for data sources for EDP, Hadoop requires the application of a patch. For additional information about enabling this support, including patching Hadoop and configuring sahara, please refer to the :doc:`hadoop-swift` documentation. Shared Filesystem support ------------------------- Sahara can also use NFS shares through the OpenStack Shared Filesystem service (manila) to store job binaries and data sources. See :doc:`edp` for more information on this feature. Orchestration support --------------------- Sahara may use the `OpenStack Orchestration engine `_ (heat) to provision nodes for clusters. For more information about enabling Orchestration usage in sahara please see :ref:`orchestration-configuration`. Plugin Capabilities ------------------- The following table provides a plugin capability matrix: +--------------------------+---------+----------+----------+-------+ | | Plugin | | +---------+----------+----------+-------+ | Feature | Vanilla | HDP | Cloudera | Spark | +==========================+=========+==========+==========+=======+ | Nova and Neutron network | x | x | x | x | +--------------------------+---------+----------+----------+-------+ | Cluster Scaling | x | Scale Up | x | x | +--------------------------+---------+----------+----------+-------+ | Swift Integration | x | x | x | x | +--------------------------+---------+----------+----------+-------+ | Cinder Support | x | x | x | x | +--------------------------+---------+----------+----------+-------+ | Data Locality | x | x | N/A | x | +--------------------------+---------+----------+----------+-------+ | EDP | x | x | x | x | +--------------------------+---------+----------+----------+-------+ Security group management ------------------------- .. TODO (mimccune) This section could use an example to show how security groups are used. Sahara allows you to control which security groups will be used for created instances. This can be done by providing the ``security_groups`` parameter for the node group or node group template. The default for this option is an empty list, which will result in the default project security group being used for the instances. Sahara may also create a security group for instances in the node group automatically. This security group will only contain open ports for required instance processes and the sahara engine. This option is useful for development and for when your installation is secured from outside environments. For production environments we recommend controlling the security group policy manually. Shared and protected resources support -------------------------------------- Sahara allows you to create resources that can be shared across tenants and protected from modifications. To provide this feature all sahara objects that can be accessed through REST API have ``is_public`` and ``is_protected`` boolean fields. They can be initially created with enabled ``is_public`` and ``is_protected`` parameters or these parameters can be updated after creation. Both fields are set to ``False`` by default. If some object has its ``is_public`` field set to ``True``, it means that it's visible not only from the tenant in which it was created, but from any other tenants too. If some object has its ``is_protected`` field set to ``True``, it means that it can not be modified (updated, scaled, canceled or deleted) unless this field is set to ``False``. Public objects created in one tenant can be used from other tenants (for example, a cluster can be created from a public cluster template which is created in another tenant), but modification operations are possible only from the tenant in which object was created.