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caddy.nix
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caddy.nix
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# Caddy is a reverse proxy, like Nginx or Traefik. This creates an ingress
# point from my local network or the public (via Cloudflare). Instead of a
# Caddyfile, I'm using the more expressive JSON config file format. This means
# I can source routes from other areas in my config and build the JSON file
# using the result of the expression.
# Caddy helpfully provides automatic ACME cert generation and management, but
# it requires a form of validation. We are using a custom build of Caddy
# (compiled with an overlay) to insert a plugin for managing DNS validation
# with Cloudflare's DNS API.
{
config,
pkgs,
lib,
...
}:
{
options = {
caddy = {
tlsPolicies = lib.mkOption {
type = lib.types.listOf lib.types.attrs;
description = "Caddy JSON TLS policies";
default = [ ];
};
routes = lib.mkOption {
type = lib.types.listOf lib.types.attrs;
description = "Caddy JSON routes for http servers";
default = [ ];
};
blocks = lib.mkOption {
type = lib.types.listOf lib.types.attrs;
description = "Caddy JSON error blocks for http servers";
default = [ ];
};
cidrAllowlist = lib.mkOption {
type = lib.types.listOf lib.types.str;
description = "CIDR blocks to allow for requests";
default = [ ];
};
};
};
config = lib.mkIf config.services.caddy.enable {
# Force Caddy to 403 if not coming from allowlisted source
caddy.cidrAllowlist = [ "127.0.0.1/32" ];
caddy.routes = lib.mkBefore [
{
match = [ { not = [ { remote_ip.ranges = config.caddy.cidrAllowlist; } ]; } ];
handle = [
{
handler = "static_response";
status_code = "403";
}
];
}
];
services.caddy =
let
default_logger_name = "other";
roll_size_mb = 25;
# Extract list of hostnames (fqdns) from current caddy routes
getHostnameFromMatch = match: if (lib.hasAttr "host" match) then match.host else [ ];
getHostnameFromRoute =
route:
if (lib.hasAttr "match" route) then (lib.concatMap getHostnameFromMatch route.match) else [ ];
hostnames_non_unique = lib.concatMap getHostnameFromRoute config.caddy.routes;
hostnames = lib.unique hostnames_non_unique;
# Create attrset of subdomains to their fqdns
hostname_map = builtins.listToAttrs (
map (hostname: {
name = builtins.head (lib.splitString "." hostname);
value = hostname;
}) hostnames
);
in
{
adapter = "''"; # Required to enable JSON
configFile = pkgs.writeText "Caddyfile" (
builtins.toJSON {
apps.http.servers.main = {
listen = [ ":443" ];
# These routes are pulled from the rest of this repo
routes = config.caddy.routes;
errors.routes = config.caddy.blocks;
# Uncommenting collects access logs
logs = {
inherit default_logger_name;
# Invert hostnames keys and values
logger_names = lib.mapAttrs' (name: value: {
name = value;
value = name;
}) hostname_map;
};
};
apps.http.servers.metrics = { }; # Enables Prometheus metrics
apps.tls.automation.policies = config.caddy.tlsPolicies;
# Setup logging to journal and files
logging.logs =
{
# System logs and catch-all
# Must be called `default` to override Caddy's built-in default logger
default = {
level = "INFO";
encoder.format = "console";
writer = {
output = "stderr";
};
exclude = (map (hostname: "http.log.access.${hostname}") (builtins.attrNames hostname_map)) ++ [
"http.log.access.${default_logger_name}"
];
};
# This is for the default access logs (anything not captured by hostname)
other = {
level = "INFO";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/other.log";
roll = true;
inherit roll_size_mb;
};
include = [ "http.log.access.${default_logger_name}" ];
};
# This is for using the Caddy API, which will probably never happen
admin = {
level = "INFO";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/admin.log";
roll = true;
inherit roll_size_mb;
};
include = [ "admin" ];
};
# This is for TLS cert management tracking
tls = {
level = "INFO";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/tls.log";
roll = true;
inherit roll_size_mb;
};
include = [ "tls" ];
};
# This is for debugging
debug = {
level = "DEBUG";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/debug.log";
roll = true;
roll_keep = 1;
inherit roll_size_mb;
};
};
}
# These are the access logs for individual hostnames
// (lib.mapAttrs (name: value: {
level = "INFO";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/${name}-access.log";
roll = true;
inherit roll_size_mb;
};
include = [ "http.log.access.${name}" ];
}) hostname_map)
# We also capture just the errors separately for easy debugging
// (lib.mapAttrs' (name: value: {
name = "${name}-error";
value = {
level = "ERROR";
encoder.format = "json";
writer = {
output = "file";
filename = "${config.services.caddy.logDir}/${name}-error.log";
roll = true;
inherit roll_size_mb;
};
include = [ "http.log.access.${name}" ];
};
}) hostname_map);
}
);
};
systemd.services.caddy.serviceConfig = {
# Allows Caddy to serve lower ports (443, 80)
AmbientCapabilities = "CAP_NET_BIND_SERVICE";
# Prevent flooding of logs by rate-limiting
LogRateLimitIntervalSec = "5s"; # Limit period
LogRateLimitBurst = 100; # Limit threshold
};
# Required for web traffic to reach this machine
networking.firewall.allowedTCPPorts = [
80
443
];
# HTTP/3 QUIC uses UDP (not sure if being used)
networking.firewall.allowedUDPPorts = [ 443 ];
# Caddy exposes Prometheus metrics with the admin API
# https://caddyserver.com/docs/api
prometheus.scrapeTargets = [ "127.0.0.1:2019" ];
};
}