Gitter Redis servers are not monitored by DataDog

All redis EC2 instances have the Datadog: monitored tag which means that Datadog should have been initialized during instance startup. However, that has not happened:

deployer@redis-persist-01:~$ dd-agent info
dd-agent: command not found

webapp output for comparison

deployer@webapp-01:~$ dd-agent info
Log file is unwritable: '/var/log/datadog/collector.log'
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Collector (v 5.32.7)
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/cc @MadLittleMods