Question-116: What is host configuration group in the Ambari?

Answer: When you create the cluster first time Ambari then initially assigns all hosts in your cluster to one default configuration group for each service which is installed. Suppose you have created 100 node cluster than all the 100 nodes would fall in the same Host configuration groups and has the same configuration.

Out of this 100 host you can take for example 25 hosts and create a different Host Configuration group and then override the default settings in this group which will be applied to all these 25 hosts if needed.

Question-117: What all are the possible alert types in the Ambari?

Answer: There are 7 different types of alerts possible in the Ambari

• Web: In this case any HTTP URL can be monitored and time out is received on that, then CRITICAL alert would be raised and notified.
• Port: This again measured in the time, how long does it take to connect on a particular port.
• Metric: example of such metric is CPU utilization for a particular node which is measured in percentage, another is RPC latency which can be measured in milliseconds.
• Aggregate: Aggregated alerts like the percent of DataNodes affected
• Script: Based on the alert a script would be executed and we can customize the response text.
• Server: It is server-side executable class to determine the status like is it OK, WARNING or CRITICAL etc.
• Recovery: Ambari agents handle the recovery alerts. So whenever process stops Ambari agent try to restart the process and based on the restart count it will raise the alert like OK, WARNING and CRITICAL.

And these for each cluster component as well as for the host. And using these alerts we can monitor the health of the cluster. Even we can give name to the alerts and provide descriptions to them, update the frequency for time to check for each alert. Once you define an alert you can enable and disable it. Above all we can group the alerts and setup the notification target like email, messaging queues for specific groups and interested team will be notified accordingly.

Question-118: What all are the severity levels in the Alerts?

Answer: There are various severity levels for alerts and the most common once are OK, WARNING, UNKNOWN and NONE. And notification of the alert would be sent only when the status of the alert changes e.g. OK to WARNING etc.