path: root/README.md

D53
===

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D53 is a dynamic DNS updater that sources information from Consul to route services to the correct place

### Tag syntax

D53 reads tags affected to services in Consul. Tags can be formatted as follows:

- `d53-a <domain> <subdomain>`, will set the node running this service as an IPv4 target in an A record for `<subdomain>.<domain>`
- `d53-aaaa <domain> <subdomain>`, same but as an IPv6 target in a AAAA record
- `d53-cname <domain> <subdomain>`, same but as an alias using a CNAME record

Example Nomad service configurations:

```hcl
# The following can be used in the Tricot service definition
# to redirect the current deuxfleurs.fr and <site_name>.site.deuxfleurs.fr
# to this node through A and AAAA records
    tags = [
           "(diplonat (tcp_port 80))"
           "d53-a deuxfleurs.fr ${meta.site}.site",
           "d53-a deuxfleurs.fr global.site",
           "d53-aaaa deuxfleurs.fr ${meta.site}.site",
           "d53-aaaa deuxfleurs.fr global.site",
         ]
```

```hcl
# The following can be used in the Guichet service definition
# to configure a Tricot reverse proxy entry, and to redirect using
# a CNAME the guichet.deuxfleurs.fr to the correct target,
# which is usually defined in the form of <site_name>.site.deuxfleurs.fr
    tags = [
           "tricot guichet.deuxfleurs.fr",
           "d53-cname deuxfleurs.fr guichet",
         ]
```

### Finding targets

The IPv4, IPv6 and CNAME targets to set in the record are extracted from the metadata values affected to each node in the Consul configuration.
In particular, the following values are used:

- `public_ipv4`: a public IPv4 through which the current node is possibly reachable (see DiploNAT to automatically open ports in a NAT)
- `public_ipv6`: a public IPv6 through which the current node is reachable
- `cname_target`: a CNAME target that resolves to a domain name whose A and/or AAAA entries point to this node (possibly among others)

Here is the relevant Nix configuration snippet that sets up these metadata values:

```nix
    let node_meta = {
        "site" = cfg.site_name;
        "public_ipv6" = cfg.ipv6;
      } //
      (if cfg.public_ipv4 != null
        then { "public_ipv4" = cfg.public_ipv4; }
        else {}) //
      (if cfg.cname_target != null
        then { "cname_target" = cfg.cname_target; }
        else {});

    ### ... later ...
    services.consul.extraConfig.node_meta = node_meta;
```