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We recently saw a major downtime on one of our app service which is deployed on azure. After analyzing the logs through app insights we found something unknown in terms of what information a metric chart provides us.
As we can see there are the dotted line and solid line chart, what does that indicate at all? The time interval where we noticed this dotted line is actually when our service was not responding at all. Any clue on this how we can know what exactly went wrong at that time?
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While platform and custom metrics are stored for 93 days, you can only query (in the Metrics tile) for a maximum of 30 days' worth of data on any single chart.
Granularity. The minimum time granularity is 1 minute, but the underlying system may capture data faster depending on the metric. For example, CPU percentage for an Azure VM is captured at a time interval of 15 seconds.
The dotted line in Azure Metrics Explorer indicates that there was no measured value (AKA “null”) between two aggregation points. For example, if in the time selector you picked “1 minute” time granularity but the metric was reported at 12:01, 12:02, 12:04, and 12:05 (note the minute gap between second and third data points), then the dotted line is shown between 12:02 and 12:04 and the solid line connects all other data points. Also, it may be useful to know that when there is no measured value, the dotted line drops down to zero when the metrics uses “Count” and “Sum” aggregation. When the aggregation is “Average”, “Minimum” or “Maximum” the dotted line simply connects two nearest known data points.
Vitaly Gorbenko
Program Manager at Microsoft Azure Monitor team
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