Statistics

• Downstream: Downstream statistics relate to incoming connections/requests. They are emitted by listeners, the HTTP connection manager, the TCP proxy filter, etc.
• Server: Server statistics describe how the Envoy server instance is working. Statistics like server uptime or amount of allocated memory are categorized here.

A single proxy scenario typically involves both downstream and upstream statistics. The two types can be used to get a detailed picture of that particular network hop. Statistics from the entire mesh give a very detailed picture of each hop and overall network health. The statistics emitted are documented in detail in the operations guide.

Within Envoy and throughout the documentation, statistics are identified by a canonical string representation. The dynamic portions of these strings are stripped to become tags. Users can configure this behavior via the Tag Specifier configuration.

• Gauges: Unsigned integers that both increase and decrease. E.g., currently active requests.

Internally, counters and gauges are batched and periodically flushed to improve performance. Histograms are written as they are received. Note: what were previously referred to as timers have become histograms as the only difference between the two representations was the units.

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