Neon DB and Fly.IO

I like Fly and NeonDB is one of their recommended managed Postges vendors, so I thought I would check them out for one of my projects.

They have a pretty good guide to setting it up in Phoenix.

Of course, I ran into issues.

The problem is, Fly uses IPv6 and Neon doesn’t support it (yet). You need to make a couple of changes to the default Dockerfile and runtime configuration.

Dockerfile

Comment out the line, added by Fly, that sets Ecto to IPV6

...

# Appended by flyctl
# ENV ECTO_IPV6 true <- Comment out this line
ENV ERL_AFLAGS "-proto_dist inet6_tcp"

Runtime.exs

1. Remove maybe_ipv6
2. Configure ssl_opts

...

  %URI{host: database_host} = URI.parse(database_url)
  # maybe_ipv6 = if System.get_env("ECTO_IPV6") in ~w(true 1), do: [:inet6], else: []
  # NOTE: explicitly set no ipv6 because fly.io was still setting ECTO_IPV6

  config :my_app, MyApp.Repo,
    ssl: true,
    url: database_url,
    ssl_opts: [
      verify: :verify_peer,
      cacertfile: Path.join(:code.priv_dir(:my_app), "cert/cacert.pem"),
      server_name_indication: to_charlist(database_host),
      customize_hostname_check: [
        match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
      ]
    ],
    pool_size: String.to_integer(System.get_env("POOL_SIZE") || "10"),
    # maybe_ipv6,
    socket_options: [],
    prepare: :unnamed

...