[Bug 1750356] Re: Apache2: BalancerMember worker hostname (65.character.host.name) too long

Andreas Hasenack andreas at canonical.com
Wed Jun 27 18:57:02 UTC 2018

** Description changed:

  If the BalancerMember directive contains a URL with a hostname longer
  than X characters, apache2 will fail to start with the following error:
  BalancerMember worker hostname (65.character.host.name) too long
  RFC1035 allows for longer hostnames, and apache upstream has this fix
  [Test Case]
  * Install the packages:
  sudo apt install apache
  * Edit /etc/apache2/sites-available/000-default.conf and add the following block inside the VirtualHost block:
    <Proxy "balancer://test">
      BalancerMember "http://xxxxxx-xx-xxxxxxxx-xxxxx-xxxxx.xx-xxxx-x.xxxxx-xxx.xxx.xxxxx.xxxx:90/"
      BalancerMember "http://xxxxxx-xx-xxxxxxxx-xxxxx-xxxxx.xx-xxxx-x.xxxxx-xxx.xxx.xxxxx.xxxx:91/"
    ProxyRequests Off
    <Proxy *>
      Order deny,allow
      Allow from all
    RewriteEngine On
    RewriteRule ^/foo balancer://test/foo [P,L]
  * Enable the necessary apache modules:
  sudo a2enmod proxy_balancer proxy lbmethod_byrequests proxy_http rewrite
  * Restart apache2, which will fail:
  sudo systemctl restart apache2
  * Run the status action and expect an error like this:
  sudo systemctl status apache2.service
  Jun 27 18:31:16 bionic-apache-1750356 apachectl[2218]: BalancerMember worker hostname (xxxxxx-xx-xxxxxxxx-xxxxx-xxxxx.xx-xxxx-x.xxxxx-xxx.xxx.xxxxx.xxxx) too long
  * Update the apache2 packages to the ones available in proposed. As part of the upgrade, apache2 will be restarted again, and in this time it will work. Confirm with systemctl status apache2 that there are no errors this time:
  sudo systemctl status apache2
  * Try to access http://localhost/foo to trigger the load balancer
  configuration. It will trigger a DNS error as we don't have an entry for
  the BalancerMember hostname, but it shows that the configuration worked:
  ubuntu at bionic-apache-1750356:~$ wget http://localhost/foo
  --2018-06-27 18:39:58--  http://localhost/foo
  Resolving localhost (localhost)...
  Connecting to localhost (localhost)||:80... connected.
  HTTP request sent, awaiting response... 502 Proxy Error
  2018-06-27 18:39:58 ERROR 502: Proxy Error.
  ubuntu at bionic-apache-1750356:~$ tail /var/log/apache2/error.log  -n 1
  [Wed Jun 27 18:39:58.732097 2018] [proxy:error] [pid 3628:tid 139981565716224] [client] AH00898: DNS lookup failure for: xxxxxx-xx-xxxxxxxx-xxxxx-xxxxx.xx-xxxx-x.xxxxx-xxx.xxx.xxxxx.xxxx returned by /foo
  [Regression Potential]
-  * discussion of how regressions are most likely to manifest as a result
- of this change.
-  * It is assumed that any SRU candidate patch is well-tested before
-    upload and has a low overall risk of regression, but it's important
-    to make the effort to think about what ''could'' happen in the
-    event of a regression.
-  * This both shows the SRU team that the risks have been considered,
-    and provides guidance to testers in regression-testing the SRU.
+ This change is twofold: it allows for longer hostnames, and apache won't fail to start anymore if that length is exceeded. In the latter case, however, the hostname is truncated. With that in mind, here are some scenarios:
+ - hostnames larger than 65 characters but less than 255: before apache2 would fail to start, now it works.
+ - hostname larger than 255 characters. Before apache would fail to start; now, it starts but truncates that hostname, logging a warning. The configuration is likely to not work due to the truncation, which will lead to DNS errors. If the admin was only relying on (re)start errors to become aware of configuration problems, he/she might miss this until it's too late. But at least the log will be clear about what happened.
+ - third party modules that use apache's mod_proxy structure might not be aware of the new hostname_ex member which can hold the longer string, since we didn't update the MODULE_MAGIC_NUMBER_MINOR number with this patchset, and will probably remain exhibiting the problem described in this bug.
  [Other Info]
+ The security team's regression test suite for apache2 (http://launchpad.net/qa-regression-testing) was run with the test packages from the PPA at https://launchpad.net/~ahasenack/+archive/ubuntu/apache-balance-member-hostname-1750356/+packages and passed: https://pastebin.ubuntu.com/p/nZ6GGHXgwQ/
-  * Anything else you think is useful to include
-  * Anticipate questions from users, SRU, +1 maintenance, security teams and the Technical Board
-  * and address these questions in advance
  == Original Description ==
  If the BalancerMember directive contains a URL with a hostname longer
  than X characters, we fail as follows:
  BalancerMember worker hostname (65.character.host.name) too long
  The size of the hostname needs to be raised so it is RFC1035 compliant.
  Bug fixed upstream at
  https://bz.apache.org/bugzilla/show_bug.cgi?id=62085, patches backported
  to v2.4.30:
  (Both patches required, first is extended by second).

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