NTP Checks

Ensure that NTP is properly set up on all nodes. Particularly for Cassandra DO NOT use anything else other than ntp. Here are some helpful blogs that explain why:

• https://blog.rapid7.com/2014/03/14/synchronizing-clocks-in-a-cassandra-cluster-pt-1-the-problem/

• https://www.digitalocean.com/community/tutorials/how-to-set-up-time-synchronization-on-ubuntu-16-04

How can I see if NTP is correctly set up?

This is an important part of your setup, particularly for your Cassandra nodes. You should use ntpd and our ansible scripts to ensure it is installed correctly - but you can still check it manually if you prefer. The following 2 sub-sections explain both approaches.

I used your ansible scripts and prefer to have automated checks

Then the easiest way is to use this ansible playbook

I am not using ansible and like to SSH into hosts and checking things manually

The following shows how to check for existing servers connected to (assumes ntpq is installed)

ntpq -pn

which should yield something like this:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time.example.    .POOL.          16 p    -   64    0    0.000    0.000   0.000
+<IP_ADDR_1>      <IP_ADDR_N>      2 u  498  512  377    0.759    0.039   0.081
*<IP_ADDR_2>      <IP_ADDR_N>      2 u  412  512  377    1.251   -0.670   0.063

if your output shows _ONLY_ the entry with a .POOL. as refid and a lot of 0s, something is probably wrong, i.e.:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time.example.    .POOL.          16 p    -   64    0    0.000    0.000   0.000

What should you do if this is the case? Ensure that ntp is installed and that the servers in the pool (typically at /etc/ntp.conf) are reachable.