The interface+mock just to test this one little error handling may seem
like overkill but there was just no other way to write an automated test
around this logic as there's no way to simluate this error with stock
Docker.
Instead of checking Consul's version on startup to see if it supports
TLSSkipVerify, assume that it does and only log in the job service
handler if we discover Consul does not support TLSSkipVerify.
The old code would break TLSSkipVerify support if Nomad started before
Consul (such as on system boot) as TLSSkipVerify would default to false
if Consul wasn't running. Since TLSSkipVerify has been supported since
Consul 0.7.2, it's safe to relax our handling.
A comment in the nomad source code states that swapping for
executor_linux allocations is disabled but it wasn't.
Nomad wrote -1 to the memsw.limit_in_bytes cgroup file to disable
swapping.
This has the following problems:
1.) Writing -1 to the file does not disable swapping. It sets
the limit for memory and swap to unlimited.
2.) On common Linux distributions like Ubuntu 16.04 LTS the
memsw.limit_in_bytes cgroup file does not exist by default.
The memsw.limit_in_bytes file only exist if the Linux kernel is
build with CONFIG_MEMCG_SWAP=yes and either
CONFIG_MEMCG_SWAP_ENABLED=yes or when the kernel parameter
swapaccount=1 is passed during boot.
Most Linux distributions disable swap accounting by default because
of higher memory usage.
Nomad silently ignores if writing to the memsw.limit_in_bytes file
fails. The allocation succeeds, no message is logged to notify the
user.
To ensure that disabling swap works on common Linux kernels, disable
swapping by writing 0 to the memory.swappiness file.
Using the memory.swappiness file only requires that the kernel is
compiled with CONFIG_MEMCG=yes. This is the default in common Linux
kernels.
