Infrastructure

This section identifies certain software and settings that contribute to your node's infrastructure.

Network Time

To keep all cluster nodes time-synchronized, MapR requires software such as a Network Time Protocol (NTP) server (or chrony for RHEL 7) to be configured and running on every node. If server clocks in the cluster drift out of sync, serious problems will occur with certain MapR services. MapR raises a Time Skew alarm on any out-of-sync nodes. For more information about obtaining and installing NTP, see http://www.ntp.org/.

Advanced: It is recommended to install an internal time server that the cluster nodes sync with directly. Using this internal time server, if internet connectivity is lost, the time on the cluster nodes still stays in sync. Refer to the preceding documentation link for NTP, for more details.

System Locale

Ensure your system locale is set to en_us. For more information about setting the system locale, see this website.

Syslog

Syslog should be enabled on each node to preserve logs regarding killed processes or failed jobs. Modern versions such as syslog-ng and rsyslog are possible, making it more difficult to be sure that a syslog daemon is present. One of the following commands should suffice:

syslogd -v
service syslog status

rsyslogd -v
service rsyslog status

Default umask

To prevent significant installation problems, ensure that the default umask for the root user is set to 0022 on all MapR nodes in the cluster. The umask setting is changed in the /etc/profile file, or in the .cshrc or .login file. The root user must have a 0022 umask because the MapR admin user requires access to all files and directories under the /opt/mapr directory, even those initially created by root services.

ulimit

ulimit is a command that sets limits on the user's access to system-wide resources. Specifically, it provides control over the resources available to the shell and to processes started by it.

The mapr-warden script uses the ulimit command to set the maximum number of file descriptors (nofile) and processes (nproc) to 64000. Higher values are unlikely to result in an appreciable performance gain. Lower values, such as the default value of 1024, are likely to result in task failures.

Warning: The MapR recommended value is set automatically every time Warden is started.

Depending on your environment, you might want to set limits manually for service accounts used to run I/O-heavy operations rather than relying on Warden to set them automatically using ulimit.

PAM

Nodes that will run the MapR Control System can take advantage of Pluggable Authentication Modules (PAM) if found. Configuration files in the /etc/pam.d/ directory are typically provided for each standard Linux command. MapR can use, but does not require, its own profile.

Security - SELinux, AppArmor

SELinux (or the equivalent on other operating systems) must be disabled during the install procedure. If the extra security provided by SELinux is required, it can be enabled in permissive mode after installation, and rules can be defined by observing regular operations while the cluster is running. Please note that SElinux introduces significant complexity and should be managed by an experienced system administrator, outside of MapR support.

TCP Retries

On each node, set TCP retries for net.ipv4.tcp_retries2 to 5 so that MapR can detect unreachable nodes with less latency.
Note: The installation automatically sets TCP retries for net.ipv4.tcp_syn_retries to 4 on each node.
  1. Edit the file /etc/sysctl.conf and add the following line:

    net.ipv4.tcp_retries2=5

  2. Save the file and run:

    sysctl -p

NFS

Disable the stock Linux NFS server on nodes that will run the MapR NFS server.

iptables/firewalld

Enabling iptables on a node may close ports that are used by MapR. If you enable iptables, make sure that required ports remain open. Check your current IP table rules with the following command:

$ service iptables status

In CentOS 7, firewalld replaces iptables. To check your current IP table rules, use this command:

systemctl status firewalld
To ensure that required ports are available, disable firewalld by using this command:
systemctl disable firewalld

Transparent Huge Pages (THP)

For data-intensive workloads, MapR recommends disabling the Transparent Huge Pages (THP) feature in the Linux kernel.

RHEL Example

$ echo never > /sys/kernel/mm/transparent_hugepage/enabled

CentOS 7 Example

echo never > /sys/kernel/mm/transparent_hugepage/enabled

Ubuntu Example

$ echo never > /sys/kernel/mm/transparent_hugepage/defrag

Automated Configuration

Some users find tools like Puppet or Chef useful to configure each node in a cluster. Make sure, however, that any configuration tool does not reset changes made when MapR packages are later installed. Specifically, do not let automated configuration tools overwrite changes to the following files:

  • /etc/sudoers
  • /etc/sysctl.conf
  • /etc/security/limits.conf
  • /etc/udev/rules.d/99-mapr-disk.rules