All three are complimentary. At Shopify we use all three for slightly different things. * Splunk searches the log files and sends alerts * NewRelic is our

All three are complimentary. At Shopify we use all three for slightly different things. * Splunk searches the log files and sends alerts * NewRelic is our always running systems profiler and our primary source for spotting performance regressions and digging into the issues * Datadog creates the dashboards and anomaly tracking, sometimes for business metrics as well. It's also a great tool to coordinate fixing incidents when they arise. Our Ops area has a massive wall of 55" screens showing all this telemetry to anyone passing by. It's wild.