Example reproduction of DNS caching issue

dns-cache-issue-example

# Create a docker network named 'frontend'
$ docker network create frontend

# Start several aliased containers that will be part of the round-robin
$ docker run -d --net frontend --net-alias example.test nginx:alpine
$ docker run -d --net frontend --net-alias example.test nginx:alpine
$ docker run -d --net frontend --net-alias example.test nginx:alpine
$ docker run -d --net frontend --net-alias example.test nginx:alpine
$ docker run -d --net frontend --net-alias example.test nginx:alpine

# Run an elixir container on the network without caching enabled,
# where inetrc file contains:
#
# {lookup, [dns, native]}.
# {cache_size, 100}.
# {cache_refresh, 60}.
#

$ docker run --rm -it -v $(pwd)/inetrc:/inetrc --net frontend elixir iex

iex(1)> Enum.map(0..4, fn _ -> :inet.getaddrs('example.test', :inet) end) 
[
  ok: [
    {172, 18, 0, 4},
    {172, 18, 0, 3},
    {172, 18, 0, 5},
    {172, 18, 0, 2},
    {172, 18, 0, 6}
  ],
  ok: [
    {172, 18, 0, 4},
    {172, 18, 0, 6},
    {172, 18, 0, 3},
    {172, 18, 0, 5},
    {172, 18, 0, 2}
  ],
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 6},
    {172, 18, 0, 4},
    {172, 18, 0, 5}
  ],
  ok: [
    {172, 18, 0, 4},
    {172, 18, 0, 6},
    {172, 18, 0, 3},
    {172, 18, 0, 5},
    {172, 18, 0, 2}
  ],
  ok: [
    {172, 18, 0, 4},
    {172, 18, 0, 3},
    {172, 18, 0, 6},
    {172, 18, 0, 2},
    {172, 18, 0, 5}
  ]
]

# Run an elixir container on the network with caching enabled
# After the initial lookup subsequent lookups return the list sorted
$ docker run --rm -it -v $(pwd)/inetrc:/inetrc --net frontend elixir iex --erl "-kernel inetrc '/inetrc'" 

iex(1)> Enum.map(0..4, fn _ -> :inet.getaddrs('example.test', :inet) end) 
[
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 4},
    {172, 18, 0, 6},
    {172, 18, 0, 5}
  ],
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 4},
    {172, 18, 0, 5},
    {172, 18, 0, 6}
  ],
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 4},
    {172, 18, 0, 5},
    {172, 18, 0, 6}
  ],
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 4},
    {172, 18, 0, 5},
    {172, 18, 0, 6}
  ],
  ok: [
    {172, 18, 0, 2},
    {172, 18, 0, 3},
    {172, 18, 0, 4},
    {172, 18, 0, 5},
    {172, 18, 0, 6}
  ]
]