This section describes and helps you troubleshoot connectivity requirements.

Fully Qualified Domain Names (FQDNs)

When you install a data-fabric cluster and you specify the host names using the data-fabric installer or the script, use fully qualified domain names (FQDNs). Do not use an alias or IP address to specify the host names. Using an IP address can prevent services such as the timeline service from verifying security certificates. In addition, monitoring services can fail after installation because of connection requests that are rejected. These issues can be difficult to troubleshoot and can be prevented by using FQDNs.

It is important to use FQDNs when configuring a secure cluster. However, the practice also applies to non-secure clusters that might later be upgraded to be secure. The same connectivity issues can be encountered when a non-secure cluster is upgraded to a secure cluster. If your cluster is non-secure and will not be secured, or if you are not concerned about connection issues for the monitoring services, you may use IP addresses to specify the host names.

Unique Hostnames

Each node in the cluster must be accessible via DNS. More specifically, each node in the cluster must have a unique hostname, resolvable forward and backward with every other node with both normal and reverse DNS name lookup.

Run hostname -f to check the node's hostname. For example:

$ hostname -f

If hostname -f returns a name, run getent hosts 'hostname' to return the node's IP address and fully-qualified domain name (FQDN).

$ getent hosts 'hostname'

To troubleshoot hostname problems, edit the /etc/hosts file as root. A simple /etc/hosts might contain:     localhost    mapr-hadoopn.maprtech.prv mapr-hadoopn

A common problem is an incorrect loopback entry (127.0.x.x) that prevents the IP address from being assigned to the hostname. For example, on Ubuntu, the default /etc/hosts file might contain:     localhost

A loopback (127.0.x.x) entry with the node's hostname will confuse the installer and other programs. Edit the /etc/hosts file and delete any entries that associate the hostname with a loopback IP. Only associate the hostname with the actual IP address.

Note: For more information about Ubuntu's default /etc/hosts file, see

Use the ping command to verify that each node can reach the others using each node's hostname. For more information, see the hosts(5) man page.

Common Users

A user that accesses the cluster must have the same credentials and user ID (uid) on each node in the cluster. Every person or department that runs data-fabric jobs must have an account and must also belong to a common group ID (gid). The uid for each user, and the gid for each group, must be consistent across all nodes.

A mapr user must exist, and have the same UID across all the cluster nodes. The mapr user has full privileges to administer the cluster. If you create the mapr user before you install data-fabric, you can test for connectivity issues. If you do not create the mapr user, installing data-fabric automatically creates the user for you. The mapr user ID is automatically created on each node if you do not use a directory service, such as LDAP.

To create a group, add a user to the group, or create the mapr user, run the following command as root substituting a uid for m and a gid for n. (The error "cannot lock /etc/passwd" suggests that the command was not run as root.)

$ useradd mapr --gid n --uid m

Example: $ groupadd -g 5000 mapr $ useradd -g 5000 -u 5000 mapr

To verify that the users or groups were created, run su mapr. Verify that a home directory was created (usually /home/mapr) and that the users or groups have read-write access to it. The users or groups must have write access to the /tmp directory, or Warden will fail to start services.

Optional: Passwordless ssh

Setting up passwordless ssh is straightforward. On each webserver node, generate a key pair and append the key to an authorization file. Then copy this authorization file to each node, so that every node is available from the webserver node.

su mapr (if you are not already logged in as mapr) ssh-keygen -t rsa -P '' -f ~/ filename

The ssh-keygen command creates filename , containing the private key, and filename .pub, containing the public key. For convenience, you may want to name the file for the hostname of the node. For example, on the node with hostname "node10.10.1.1,"

ssh-keygen -t rsa -P '' -f ~/node10.10.1.1

In this example, append the file /home/mapr/ to the authorized_keys file.

Append each webserver node's public key to a single file, using a command such as cat filename .pub >> authorized_keys. (The key file is simple text, so you can append the file in several ways, including a text editor.) When every webserver node's empty passphrase public key has been generated, and the public key file has been appended to the master "authorized_keys" file, copy this master keys file to each node as ~/.ssh/authorized_keys, where ~ refers to the mapr user's home directory (typically /home/mapr).

Recommended: Setting the MAPR_SUBNETS Variable

For enhanced performance and reliability, always set the MAPR_SUBNETS enivronment variable.