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ggreenway merged 5 commits into from
Aug 12, 2021
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hot_restart.rst: update outdated detailed information #17653

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hot_restart.rst: update outdated detailed information
qinggniq Aug 10, 2021
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qinggniq Aug 11, 2021
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qinggniq Aug 11, 2021
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qinggniq Aug 12, 2021
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4 changes: 1 addition & 3 deletions docs/root/intro/arch_overview/operations/hot_restart.rst
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Expand Up @@ -9,10 +9,8 @@ Envoy can fully reload itself (both code and configuration) without dropping exi
during the :ref:`drain process <arch_overview_draining>`. The hot restart functionality has the
following general architecture:

* Statistics and some locks are kept in a shared memory region. This means that gauges will be
consistent across both processes as restart is taking place.
* The two active processes communicate with each other over unix domain sockets using a basic RPC
protocol.
protocol. Statistics will be transported from the old process to the new process over the unix domain.

@ramaraochavali ramaraochavali Aug 10, 2021

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We do not transport all stats - It would be good to qualify

@qinggniq qinggniq Aug 10, 2021

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Do you mean counters and gauges?

@ramaraochavali ramaraochavali Aug 10, 2021

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yes. For example, all gauges are not transported

@qinggniq qinggniq Aug 10, 2021

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AFAIK, during hot restart, all counters and gauges will be transported to the new process, but after the new process sending the terminate request, the new process will clean up the contributions of most gauges transported from the old process except hot_restart_generation stat. Am I misunderstand?

@mattklein123 mattklein123 Aug 10, 2021

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Some gauges are transported and some are not. Each gauge is marked as never import, import, etc.

* The new process fully initializes itself (loads the configuration, does an initial service
discovery and health checking phase, etc.) before it asks for copies of the listen sockets from
the old process. The new process starts listening and then tells the old process to start
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