Our dnsmasq configuration needs host-specific data that we can't configure in
the AMI build. But configuring this in userdata leads to a race between
userdata execution, docker.service startup, and dnsmasq.service startup. So
rather than letting dnsmasq come up with incorrect configuration and then
modifying it after the fact, do the configuration in the service's prestart,
and have it kick off a Docker restart when we're done.
The cloud-init configuration runs on boot, which can result in a race
condition between that and service startup. This has caused provisioning
failures because Nomad expects the userdata to have configured a host volume
directory. Diagnosing this was also compounded by a warning being fired by
systemd for the Nomad unit file.
* Update the location of the `StartLimitIntervalSec` field to it's
post-systemd-230 location.
* Ensure that the weekly AMI build is up-to-date to reduce the risk of
unexpected system software changes.
* Move the host volume to a directory we can set up at AMI build time rather
than in userdata.
Newer EC2 instances are both cheaper and have generally better
performance.
The dnsmasq configuration had a hard-coded interface name, so in order to
accomodate instances with more recent networking that result in so-called
predictable interface names, the dnsmasq configuration needs to be replaced at
runtime with userdata to select the default interface.
* remove outdated references to envchain in documentation
* add new host volume locations in userdata
* don't exit the entire script during provisioning, just return
