Jeff Elsloo created TC-401:
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Summary: Traffic Router Serves OFFLINE Caches
Key: TC-401
URL: https://issues.apache.org/jira/browse/TC-401
Project: Traffic Control
Issue Type: Bug
Components: Traffic Router
Affects Versions: 2.0.0
Reporter: Jeff Elsloo
Fix For: 2.1.0
We identified an issue that causes Traffic Router to serve up an {{OFFLINE}}
cache indefinitely after a snapshot of the CRConfig. This bug will also do the
inverse, where a cache that was previously set to {{OFFLINE}} will never have
traffic routed to it when set back to {{ONLINE}} or {{REPORTED}} (referenced
only as {{ONLINE}} henceforth).
The bug is caused by {{ConfigHandler.processConfig()}} clearing the cache
locations from the {{NetworkNode}} prior to swapping out the instance of
{{CacheRegister}}. When the cache locations have been cleared, but the prior
{{CacheRegister}} is still in place, a race condition can occur where the
{{CacheLocation}} for a given cache group from the prior config will be set on
the recently cleared {{NetworkNode}}. When this happens, the {{List<Cache>}}
contains the prior config's list for that cache group, which means that any
host state change from/to {{ONLINE}} or {{OFFLINE}} will not be reflected. This
is because when transitioning to {{OFFLINE}} the {{Cache}} drops from the
CRConfig and it will reappear when set to {{ONLINE}}. Contrast this with
{{ONLINE}} to {{ADMIN_DOWN}}, the {{Cache}} remains in the CRConfig, so we are
simply using the status to determine whether the cache is available and the
software works as designed.
This is due to the way we use lazy loading to associate network ranges within
the CZF with {{CacheLocations}} within a given {{NetworkNode}} representing
that section of the CZF. In {{TrafficRouter}}, during cache selection, if we
have a hit in the coverage zone file but the {{CacheLocation}} is
uninitialized, we obtain the {{CacheLocation}} from {{CacheRegister}} and set
it for that specific {{NetworkNode}}. If our {{NetworkNode}} is cleared but our
{{CacheRegister}} has yet to be swapped, we will set the {{NetworkNode}} to the
old {{CacheLocation}} and as mentioned, which will have a reference to the
prior {{List<Cache>}}, denying anyone the opportunity to populate that
{{NetworkNode}} with the new {{CacheLocation}} and new {{List<Cache>}}.
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