driver/docker: protect against nil container #7749
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Protect against a panic when we attempt to start a container with a name that conflicts with an existing one. If the existing one is being deleted while nomad first attempts to create the container, the createContainer will fail with `container already exists`, but we get nil container reference from the `containerByName` lookup, and cause a crash. I'm not certain how we get into the state, except for being very unlucky. I suspect that this case may be the result of a concurrent restart or the docker engine API not being fully consistent (e.g. an earlier call purged the container, but docker didn't free up resources yet to create a new container with the same name immediately yet). If that's the case, then re-attempting creation will hopefully succeed, or we'd at least fail enough times for the alloc to be rescheduled to another node.
nickethier
approved these changes
Apr 20, 2020
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Protect against a panic when we attempt to start a container with a name
that conflicts with an existing one. If the existing one is being
deleted while nomad first attempts to create the container, the
createContainer will fail with
container already exists, but we getnil container reference from the
containerByNamelookup, and cause acrash.
I'm not certain how we get into the state, except for being very
unlucky. I suspect that this case may be the result of a concurrent
restart or the docker engine API not being fully consistent (e.g. an
earlier call purged the container, but docker didn't free up resources
yet to create a new container with the same name immediately yet).
If that's the case, then re-attempting creation will hopefully succeed,
or we'd at least fail enough times for the alloc to be rescheduled to
another node.
Fixes #7738