diff options
Diffstat (limited to 'modules/prefill')
| -rw-r--r-- | modules/prefill/README.rst | 41 | ||||
| -rw-r--r-- | modules/prefill/prefill.lua | 208 | ||||
| -rw-r--r-- | modules/prefill/prefill.mk | 2 |
3 files changed, 251 insertions, 0 deletions
diff --git a/modules/prefill/README.rst b/modules/prefill/README.rst new file mode 100644 index 0000000..e30e0c3 --- /dev/null +++ b/modules/prefill/README.rst @@ -0,0 +1,41 @@ +.. _mod-prefill: + +Cache prefilling +---------------- + +This module provides ability to periodically prefill DNS cache by importing root zone data obtained over HTTPS. + +Intended users of this module are big resolver operators which will benefit from decreased latencies and smaller amount of traffic towards DNS root servets. + +Example configuration is: + +.. code-block:: lua + + modules.load('prefill') + prefill.config({ + ['.'] = { + url = 'https://www.internic.net/domain/root.zone', + ca_file = '/etc/pki/tls/certs/ca-bundle.crt', + interval = 86400 -- seconds + } + }) + +This configuration downloads zone file from URL `https://www.internic.net/domain/root.zone` and imports it into cache every 86400 seconds (1 day). The HTTPS connection is authenticated using CA certificate from file `/etc/pki/tls/certs/ca-bundle.crt` and signed zone content is validated using DNSSEC. + +Root zone to import must be signed using DNSSEC and the resolver must have valid DNSSEC configuration. (For further details please see :ref:`enabling-dnssec`.) + +.. csv-table:: + :header: "Parameter", "Description" + + "ca_file", "path to CA certificate bundle used to authenticate the HTTPS connection" + "interval", "number of seconds between zone data refresh attempts" + "url", "URL of a file in :rfc:`1035` zone file format" + +Only root zone import is supported at the moment. + +Dependencies +^^^^^^^^^^^^ + +Depends on the luasec_ library. + +.. _luasec: https://luarocks.org/modules/brunoos/luasec diff --git a/modules/prefill/prefill.lua b/modules/prefill/prefill.lua new file mode 100644 index 0000000..c573ed9 --- /dev/null +++ b/modules/prefill/prefill.lua @@ -0,0 +1,208 @@ +local https = require('ssl.https') +local ltn12 = require('ltn12') +local lfs = require('lfs') + +local rz_url = "https://www.internic.net/domain/root.zone" +local rz_local_fname = "root.zone" +local rz_ca_file = nil +local rz_event_id = nil + +local rz_default_interval = 86400 +local rz_https_fail_interval = 600 +local rz_no_ta_interval = 600 +local rz_cur_interval = rz_default_interval +local rz_interval_randomizator_limit = 10 +local rz_interval_threshold = 5 +local rz_interval_min = 3600 + +local prefill = { +} + + +-- Fetch over HTTPS with peert cert checked +local function https_fetch(url, ca_file) + assert(string.match(url, '^https://')) + assert(ca_file) + + local resp = {} + local r, c = https.request{ + url = url, + verify = {'peer', 'fail_if_no_peer_cert' }, + cafile = ca_file, + protocol = 'tlsv1_2', + sink = ltn12.sink.table(resp), + } + if r == nil then + return r, c + end + return resp, "[prefill] "..url.." downloaded" +end + +-- Write zone to a file +local function zone_write(zone, fname) + local file, errmsg = io.open(fname, 'w') + if not file then + error(string.format("[prefill] unable to open file %s (%s)", + fname, errmsg)) + end + for i = 1, #zone do + local zone_chunk = zone[i] + file:write(zone_chunk) + end + file:close() +end + +local function display_delay(time) + local days = math.floor(time / 86400) + local hours = math.floor((time % 86400) / 3600) + local minutes = math.floor((time % 3600) / 60) + local seconds = math.floor(time % 60) + if days > 0 then + return string.format("%d days %02d hours", days, hours) + elseif hours > 0 then + return string.format("%02d hours %02d minutes", hours, minutes) + elseif minutes > 0 then + return string.format("%02d minutes %02d seconds", minutes, seconds) + end + return string.format("%02d seconds", seconds) +end + +-- returns: number of seconds the file is valid for +-- 0 indicates immediate download +local function get_file_ttl(fname) + local attrs = lfs.attributes(fname) + if attrs then + local age = os.time() - attrs.modification + return math.max( + rz_cur_interval - age, + 0) + else + return 0 -- file does not exist, download now + end +end + +local function download(url, fname) + log("[prefill] downloading root zone...") + local rzone, err = https_fetch(url, rz_ca_file) + if rzone == nil then + error(string.format("[prefill] fetch of `%s` failed: %s", url, err)) + end + + log("[prefill] saving root zone...") + zone_write(rzone, fname) +end + +local function import(fname) + local res = cache.zone_import(fname) + if res.code == 1 then -- no TA found, wait + error("[prefill] no trust anchor found for root zone, import aborted") + elseif res.code == 0 then + log("[prefill] root zone successfully parsed, import started") + else + error(string.format("[prefill] root zone import failed (%s)", res.msg)) + end +end + +local function timer() + local file_ttl = get_file_ttl(rz_local_fname) + + if file_ttl > rz_interval_threshold then + log("[prefill] root zone file valid for %s, reusing data from disk", + display_delay(file_ttl)) + else + local ok, errmsg = pcall(download, rz_url, rz_local_fname) + if not ok then + rz_cur_interval = rz_https_fail_interval + - math.random(rz_interval_randomizator_limit) + log("[prefill] cannot download new zone (%s), " + .. "will retry root zone download in %s", + errmsg, display_delay(rz_cur_interval)) + event.reschedule(rz_event_id, rz_cur_interval * sec) + return + end + file_ttl = rz_default_interval + end + -- file is up to date, import + -- import/filter function gets executed after resolver/module + local ok, errmsg = pcall(import, rz_local_fname) + if not ok then + rz_cur_interval = rz_no_ta_interval + - math.random(rz_interval_randomizator_limit) + log("[prefill] root zone import failed (%s), retry in %s", + errmsg, display_delay(rz_cur_interval)) + else + -- re-download before TTL expires + rz_cur_interval = (file_ttl - rz_interval_threshold + - math.random(rz_interval_randomizator_limit)) + log("[prefill] root zone refresh in %s", + display_delay(rz_cur_interval)) + end + event.reschedule(rz_event_id, rz_cur_interval * sec) +end + +function prefill.init() + math.randomseed(os.time()) +end + +function prefill.deinit() + if rz_event_id then + event.cancel(rz_event_id) + rz_event_id = nil + end +end + +-- process one item from configuration table +-- right now it supports only root zone because +-- prefill module uses global variables +local function config_zone(zone_cfg) + if zone_cfg.interval then + zone_cfg.interval = tonumber(zone_cfg.interval) + if zone_cfg.interval < rz_interval_min then + error(string.format('[prefill] refresh interval %d s is too short, ' + .. 'minimal interval is %d s', + zone_cfg.interval, rz_interval_min)) + end + rz_default_interval = zone_cfg.interval + rz_cur_interval = zone_cfg.interval + end + + if not zone_cfg.ca_file then + error('[prefill] option ca_file must point ' + .. 'to a file with CA certificate(s) in PEM format') + end + rz_ca_file = zone_cfg.ca_file + + if not zone_cfg.url or not string.match(zone_cfg.url, '^https://') then + error('[prefill] option url must contain a ' + .. 'https:// URL of a zone file') + else + rz_url = zone_cfg.url + end +end + +function prefill.config(config) + local root_configured = false + if not config or type(config) ~= 'table' then + error('[prefill] configuration must be in table ' + .. '{owner name = {per-zone config}}') + end + for owner, zone_cfg in pairs(config) do + if owner ~= '.' then + error('[prefill] only root zone can be imported ' + .. 'at the moment') + else + config_zone(zone_cfg) + root_configured = true + end + end + if not root_configured then + error('[prefill] this module version requires configuration ' + .. 'for root zone') + end + + -- ability to change intervals + prefill.deinit() + rz_event_id = event.after(0, timer) +end + +return prefill diff --git a/modules/prefill/prefill.mk b/modules/prefill/prefill.mk new file mode 100644 index 0000000..7b10ba9 --- /dev/null +++ b/modules/prefill/prefill.mk @@ -0,0 +1,2 @@ +prefill_SOURCES := prefill.lua +$(call make_lua_module,prefill) |