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[#144269245] Set MTU for Garden containers back to 1500 and add test #887

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merged 2 commits into from Apr 26, 2017

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commented Apr 25, 2017

What

garden-runc 1.3.0, which was included by the CF upgrade in 46019be, changed
the MTU of Guardian containers to match the host's external network
interface instead of always being 1500:

For our cells on AWS this meant a change from 1500 to 9001:

This didn't work well with IPsec, which we use to secure web traffic between
the routers and cells. Requests which generated responses larger than approx
9000 bytes were too large after the IPsec headers were added and never made
it back to the router.

It might have been nice to set this to a value a bit smaller than 9000, to
allow for the IPsec overhead, but we can't guarantee the MTU value of the
host interface because it gets set by AWS.

Ideally PMTU should mean that we wouldn't have to do this. We think that the
ICMP unreachable messages might not be getting back to the container (or
host?) correctly. It might be that we can revert this commit in future after
some more investigation.

Includes an acceptance test that:

Check that requests don't hang when the HTTP response is large (up to
200kB). This should prevent regressions of the MTU problem described in the
preceding commit.

How to review

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This must not be deployed before #884 but it should be safe if they are deployed at the same time
馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵 馃悵

  1. Code review
  2. Deploy
  3. Confirm that availability-tests pass meaning that containers were migrated correctly
  4. Confirm that custom-acceptance-tests pass meaning that larger response sizes work

Who can review

Not @saliceti or @dcarley

@paroxp paroxp self-assigned this Apr 25, 2017

@paroxp

paroxp approved these changes Apr 26, 2017

dcarley and others added some commits Apr 24, 2017

Set MTU for Garden containers back to 1500
garden-runc 1.3.0, which was included by the CF upgrade in 46019be, changed
the MTU of Guardian containers to match the host's external network
interface instead of always being 1500:

- cloudfoundry/guardian@af8d612
- cloudfoundry/garden-runc-release@a9b22fd

For our cells on AWS this meant a change from 1500 to 9001:

- http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/network_mtu.html#jumbo_frame_instances

This didn't work well with IPsec, which we use to secure web traffic between
the routers and cells. Requests which generated responses larger than approx
9000 bytes were too large after the IPsec headers were added and never made
it back to the router.

It might have been nice to set this to a value a *bit* smaller than 9000, to
allow for the IPsec overhead, but we can't guarantee the MTU value of the
host interface because it gets set by AWS.

Ideally PMTU should mean that we wouldn't have to do this. We think that the
ICMP unreachable messages might not be getting back to the container (or
host?) correctly. It might be that we can revert this commit in future after
some more investigation.
Acceptance test for large HTTP responses
Check that requests don't hang when the HTTP response is large (up to
200kB). This should prevent regressions of the MTU problem described in the
preceding commit.

@paroxp paroxp force-pushed the mtu_and_dora branch from 8e2bb01 to b192f29 Apr 26, 2017

@paroxp paroxp merged commit b192f29 into master Apr 26, 2017

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paroxp added a commit that referenced this pull request Apr 26, 2017

Merge pull request #887 from alphagov/mtu_and_dora
[#144269245] Set MTU for Garden containers back to 1500 and add test

@paroxp paroxp deleted the mtu_and_dora branch Apr 26, 2017

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