Consul config setting ports with a variable

Consul
1

Hi All,

I am trying to configure Consul (and then after that Nomad) with a ports section in my hcl config file that resolves ENV vars for the values:

Eg:

ports {
  server = "$SERVER_RPC_PORT"
  serf = "$SERF_LAN_PORT"
  http = "$API_HTTP_PORT"
  https = "$API_HTTPS_PORT"
  dns = "$CONSUL_DNS_PORT"
}

My problem is that I hit a catch-22 with this config:

  • If I don’t quote the variable references, I get an invalid token error when the parser encounters the ‘$’ in the variable reference.
  • If I do quote the variable reference, then I get a schema error saying the value must be an int.
    ** Sadly, it does not seem to attempt to coerce the string value to an int.

I tried finding the reference info on what other forms of variable interpolation is valid in the hcl files in general, and the ports {} section in particular.

Can anyone please point me to documentation on the suppprted interpolation syntax so I can work out how to resolve my var references?

Kind Regards,
Nik

2

I’m pretty sure there is no interpolation syntax at all, unless I’ve totally missed something in the documentation.

3

Well, the Consul docs show that go-template interpolcation is supported for at least some values:

bind_addr = "{{ GetPrivateInterfaces | include \"network\" \"10.0.0.0/8\" | attr \"address\" }}"

So I was hoping to find out what other functions and operators were supported by that syntax.

[Removed comment about nomad which referred to job files, and not config files]

I agree that the documentation does not state whether or not variable iterpolation is supported in general for values in the consul config file.

4

I’m pretty sure that interpolation is not a general feature of the configuration file, but a feature applied after parsing, to the literal string assigned to selected settings of “socket address” type.

5

Thanks Max - that’s pretty much as I had feared.

Do you think it’s worth raising a feature-request for some form of interpolation of values in the config file?

6

It doesn’t hurt to ask, but I’d estimate the chances of it actually happening to be low.

I think it could turn out to be surprisingly complicated to work out a way to introduce just enough of the concepts from a more complex dialect of HCL like that used by Terraform, into the config file syntax, without the engineering effort just being too hard for the limited payoff.

7

After some reading - it would seem that it could be accomplished for HCL config files by switching the config file parser from HCL1 to HCL2.
I’m still not sure about JSON config files.