Setting Up HDFS Services Using Cloudera API [Part 3]

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linux cloudera hadoop cloudera-api zookeeper hdfs

This is the second follow up post. In the earlier post

Now we will be installing the HDFS service to our cluster.

  1. Create a cluster.
  2. Install HDFS service to our cluster.

Creating a Cluster and setting up parcel is part of earlier post.

Install HDFS Service.

HDFS service is installed in stages.

  1. Create a HDFS service (if not exist).
  2. Update configuration for our newly create HDFS service.
  3. Create HDFS roles (NAMENODE, SECONDARYNAMENODE, DATANODE, GATEWAY) on the Cluster.
  4. Format Namenode.
  5. Start HDFS service.
  6. Create Temporary /tmp directory in HDFS

Create a HDFS service.

This is simple create a service if it does not exist.

def create_service(cluster):
    try:
        zk_service = cluster.get_service('HDFS')
        logging.debug("Service {0} already present on the cluster".format('HDFS'))
    except ApiException:
        #
        # Create service if it the first time.
        #
        zk_service = cluster.create_service('HDFS', 'HDFS')
        logging.info("Created New Service: HDFS")

    return zk_service

Update configuration for HDFS.

This information is picked up from the configuration yaml file.

yaml file.

  HDFS:
    config:
      dfs_replication: 3
      dfs_permissions: false
      dfs_block_local_path_access_user: impala,hbase,mapred,spark
    roles:
      - group: NAMENODE
        hosts:
          - mycmhost.ahmed.com
        config:
          dfs_name_dir_list: /data/1/dfs/nn,/data/2/dfs/nn
          dfs_namenode_handler_count: 30
      - group: SECONDARYNAMENODE
        hosts:
          - mycmhost.ahmed.com
        config:
          fs_checkpoint_dir_list: /data/1/dfs/snn,/data/2/dfs/snn

      - group: DATANODE
        hosts:
          - mycmhost.ahmed.com
        config:
          dfs_data_dir_list: /data/1/dfs/dn,/data/2/dfs/dn
          dfs_datanode_handler_count: 30
          #dfs_datanode_du_reserved: 1073741824
          dfs_datanode_failed_volumes_tolerated: 0
          dfs_datanode_data_dir_perm: 755
      - group: GATEWAY
        hosts:
          - mycmhost.ahmed.com
        config:
          dfs_client_use_trash: true

Code snippet.

def service_update_configuration(zk_service):
    """
        Update service configurations
    :return:
    """
    zk_service.update_config(config['services']['HDFS']['config'])
    logging.info("Service Configuration Updated.")

Create HDFS roles (NAMENODE, SECONDARYNAMENODE, DATANODE, GATEWAY) on the Cluster.

To create all the roles.

  • Each role needs to be unique on each host.
  • We create a unique role_name for each node.

Each role is unique based on below set of strings. (service_name, group, role_id)

role_name = '{0}-{1}-{2}'.format(service_name, group, role_id)

Here is the code snippet.

def hdfs_create_cluster_services(config, service, service_name):
    """
        Creating Cluster services
    :return:
    """

    #
    # Get the role config for the group
    # Update group configuration and create roles.
    #
    for role in config['services'][service_name]['roles']:
        role_group = service.get_role_config_group("{0}-{1}-BASE".format(service_name, role['group']))
        #
        # Update the group's configuration.
        # [https://cloudera.github.io/cm_api/epydoc/5.10.0/cm_api.endpoints.role_config_groups.ApiRoleConfigGroup-class.html#update_config]
        #
        role_group.update_config(role.get('config', {}))
        #
        # Create roles now.
        #
        hdfs_create_roles(service, service_name, role, role['group'])
        
def hdfs_create_roles(service, service_name, role, group):
    """
    Create individual roles for all the hosts under a specific role group

    :param role: Role configuration from yaml
    :param group: Role group name
    """
    role_id = 0
    for host in role.get('hosts', []):
        role_id += 1
        role_name = '{0}-{1}-{2}'.format(service_name, group, role_id)
        logging.info("Creating Role name as: " + str(role_name))
        try:
            service.get_role(role_name)
        except ApiException:
            service.create_role(role_name, group, host)        

Format Namenode.

First time when we create a HDFS environment we need to format namenode, this init the HDFS cluster. format_hdfs method returns as ApiCommand which we can track progress of execution.

def format_namenode(hdfs_service, namenode):
    try:
        #
        # Formatting HDFS - this will have no affect the second time it runs.
        # Format NameNode instances of an HDFS service.
        #
        # https://cloudera.github.io/cm_api/epydoc/5.10.0/cm_api.endpoints.services.ApiService-class.html#format_hdfs
        #

        cmd = hdfs_service.format_hdfs(namenode)[0]
        logging.debug("Command Response: " + str(cmd))
        if not cmd.wait(300).success:
            print "WARNING: Failed to format HDFS, attempting to continue with the setup"
    except ApiException:
        logging.info("HDFS cannot be formatted. May be already in use.")

Start HDFS service

We do this using the service.start() method. This method return ApiCommand which we can track the progress and wait for the service to start using cmd.wait().success More details about the Api here

Our service should be up and running.

Finally Creating /tmp directory on HDFS.

When we create a HDFS cluster we create a /tmp directory, HDFS /tmp directory is used as a temporary storage during mapreduce operation. Mapreduce artifacts, intermediate data will be kept under this directory. If we delete the /tmp contents then any MR jobs currently running will loose its current intermediate data.

Any MR run after the /tmp is clear will still work without any issues.

Creating /tmp is done using create_hdfs_tmp method which returns ApiCommand response.

Code Location

Code - Setting Up HDFS Services Using Cloudera API [Part 3]

Written on February 8, 2017