Using multiple NTP servers (#6173)

* Small improvements to time estimation. * Allow multiple NTP servers to be used. * Removing boxing. * Be nice. * Be nicer. * Update list of servers and add reference.
2017-08-09 08:45:07 +02:00 · 2017-08-09 08:45:07 +02:00 · e93466c897
commit e93466c897
parent 72fa6a79a2
11 changed files with 188 additions and 78 deletions
--- a/dapps/src/api/api.rs
+++ b/dapps/src/api/api.rs
@ -21,7 +21,7 @@ use hyper::method::Method;
 use hyper::status::StatusCode;

 use api::{response, types};
-use api::time::TimeChecker;
+use api::time::{TimeChecker, MAX_DRIFT};
 use apps::fetcher::Fetcher;
 use handlers::{self, extract_url};
 use endpoint::{Endpoint, Handler, EndpointPath};
@ -122,7 +122,6 @@ impl RestApiRouter {

 			// Check time
 			let time = {
-				const MAX_DRIFT: i64 = 500;
 				let (status, message, details) = match time {
 					Ok(Ok(diff)) if diff < MAX_DRIFT && diff > -MAX_DRIFT => {
 						(HealthStatus::Ok, "".into(), diff)
--- a/dapps/src/api/time.rs
+++ b/dapps/src/api/time.rs
@ -33,11 +33,13 @@

 use std::io;
 use std::{fmt, mem, time};
-use std::sync::Arc;
 use std::collections::VecDeque;
+use std::sync::atomic::{self, AtomicUsize};
+use std::sync::Arc;

 use futures::{self, Future, BoxFuture};
-use futures_cpupool::CpuPool;
+use futures::future::{self, IntoFuture};
+use futures_cpupool::{CpuPool, CpuFuture};
 use ntp;
 use time::{Duration, Timespec};
 use util::RwLock;
@ -45,6 +47,8 @@ use util::RwLock;
 /// Time checker error.
 #[derive(Debug, Clone, PartialEq)]
 pub enum Error {
+	/// No servers are currently available for a query.
+	NoServersAvailable,
 	/// There was an error when trying to reach the NTP server.
 	Ntp(String),
 	/// IO error when reading NTP response.
@ -56,6 +60,7 @@ impl fmt::Display for Error {
 		use self::Error::*;

 		match *self {
+			NoServersAvailable => write!(fmt, "No NTP servers available"),
 			Ntp(ref err) => write!(fmt, "NTP error: {}", err),
 			Io(ref err) => write!(fmt, "Connection Error: {}", err),
 		}
@ -72,41 +77,93 @@ impl From<ntp::errors::Error> for Error {

 /// NTP time drift checker.
 pub trait Ntp {
+	/// Returned Future.
+	type Future: IntoFuture<Item=Duration, Error=Error>;
+
 	/// Returns the current time drift.
-	fn drift(&self) -> BoxFuture<Duration, Error>;
+	fn drift(&self) -> Self::Future;
+}
+
+const SERVER_MAX_POLL_INTERVAL_SECS: u64 = 60;
+#[derive(Debug)]
+struct Server {
+	pub address: String,
+	next_call: RwLock<time::Instant>,
+	failures: AtomicUsize,
+}
+
+impl Server {
+	pub fn is_available(&self) -> bool {
+		*self.next_call.read() < time::Instant::now()
+	}
+
+	pub fn report_success(&self) {
+		self.failures.store(0, atomic::Ordering::SeqCst);
+		self.update_next_call(1)
+	}
+
+	pub fn report_failure(&self) {
+		let errors = self.failures.fetch_add(1, atomic::Ordering::SeqCst);
+		self.update_next_call(1 << errors)
+	}
+
+	fn update_next_call(&self, delay: usize) {
+		*self.next_call.write() = time::Instant::now() + time::Duration::from_secs(delay as u64 * SERVER_MAX_POLL_INTERVAL_SECS);
+	}
+}
+
+impl<T: AsRef<str>> From<T> for Server {
+	fn from(t: T) -> Self {
+		Server {
+			address: t.as_ref().to_owned(),
+			next_call: RwLock::new(time::Instant::now()),
+			failures: Default::default(),
+		}
+	}
 }

 /// NTP client using the SNTP algorithm for calculating drift.
 #[derive(Clone)]
 pub struct SimpleNtp {
-	address: Arc<String>,
+	addresses: Vec<Arc<Server>>,
 	pool: CpuPool,
 }

 impl fmt::Debug for SimpleNtp {
 	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-		write!(f, "Ntp {{ address: {} }}", self.address)
+		f
+			.debug_struct("SimpleNtp")
+			.field("addresses", &self.addresses)
+			.finish()
 	}
 }

 impl SimpleNtp {
-	fn new(address: &str, pool: CpuPool) -> SimpleNtp {
+	fn new<T: AsRef<str>>(addresses: &[T], pool: CpuPool) -> SimpleNtp {
 		SimpleNtp {
-			address: Arc::new(address.to_owned()),
+			addresses: addresses.iter().map(Server::from).map(Arc::new).collect(),
 			pool: pool,
 		}
 	}
 }

 impl Ntp for SimpleNtp {
-	fn drift(&self) -> BoxFuture<Duration, Error> {
-		let address = self.address.clone();
-		if &*address == "none" {
-			return futures::future::err(Error::Ntp("NTP server is not provided.".into())).boxed();
-		}
+	type Future = future::Either<
+		CpuFuture<Duration, Error>,
+		future::FutureResult<Duration, Error>,
+	>;

-		self.pool.spawn_fn(move || {
-			let packet = ntp::request(&*address)?;
+	fn drift(&self) -> Self::Future {
+		use self::future::Either::{A, B};
+
+		let server = self.addresses.iter().find(|server| server.is_available());
+		server.map(|server| {
+			let server = server.clone();
+			A(self.pool.spawn_fn(move || {
+				debug!(target: "dapps", "Fetching time from {}.", server.address);
+
+				match ntp::request(&server.address) {
+					Ok(packet) => {
 						let dest_time = ::time::now_utc().to_timespec();
 						let orig_time = Timespec::from(packet.orig_time);
 						let recv_time = Timespec::from(packet.recv_time);
@ -114,16 +171,29 @@ impl Ntp for SimpleNtp {

 						let drift = ((recv_time - orig_time) + (transmit_time - dest_time)) / 2;

+						server.report_success();
 						Ok(drift)
-		}).boxed()
+					},
+					Err(err) => {
+						server.report_failure();
+						Err(err.into())
+					},
+				}
+			}))
+		}).unwrap_or_else(|| B(future::err(Error::NoServersAvailable)))
 	}
 }

 // NOTE In a positive scenario first results will be seen after:
-// MAX_RESULTS * UPDATE_TIMEOUT_OK_SECS seconds.
-const MAX_RESULTS: usize = 7;
-const UPDATE_TIMEOUT_OK_SECS: u64 = 30;
-const UPDATE_TIMEOUT_ERR_SECS: u64 = 2;
+// MAX_RESULTS * UPDATE_TIMEOUT_INCOMPLETE_SECS seconds.
+const MAX_RESULTS: usize = 4;
+const UPDATE_TIMEOUT_OK_SECS: u64 = 6 * 60 * 60;
+const UPDATE_TIMEOUT_WARN_SECS: u64 = 15 * 60;
+const UPDATE_TIMEOUT_ERR_SECS: u64 = 60;
+const UPDATE_TIMEOUT_INCOMPLETE_SECS: u64 = 10;
+
+/// Maximal valid time drift.
+pub const MAX_DRIFT: i64 = 500;

 #[derive(Debug, Clone)]
 /// A time checker.
@ -134,13 +204,13 @@ pub struct TimeChecker<N: Ntp = SimpleNtp> {

 impl TimeChecker<SimpleNtp> {
 	/// Creates new time checker given the NTP server address.
-	pub fn new(ntp_address: String, pool: CpuPool) -> Self {
+	pub fn new<T: AsRef<str>>(ntp_addresses: &[T], pool: CpuPool) -> Self {
 		let last_result = Arc::new(RwLock::new(
 			// Assume everything is ok at the very beginning.
 			(time::Instant::now(), vec![Ok(0)].into())
 		));

-		let ntp = SimpleNtp::new(&ntp_address, pool);
+		let ntp = SimpleNtp::new(ntp_addresses, pool);

 		TimeChecker {
 			ntp,
@ -149,22 +219,34 @@ impl TimeChecker<SimpleNtp> {
 	}
 }

-impl<N: Ntp> TimeChecker<N> {
+impl<N: Ntp> TimeChecker<N> where <N::Future as IntoFuture>::Future: Send + 'static {
 	/// Updates the time
 	pub fn update(&self) -> BoxFuture<i64, Error> {
+		trace!(target: "dapps", "Updating time from NTP.");
 		let last_result = self.last_result.clone();
-		self.ntp.drift().then(move |res| {
+		self.ntp.drift().into_future().then(move |res| {
+			let res = res.map(|d| d.num_milliseconds());
+
+			if let Err(Error::NoServersAvailable) = res {
+				debug!(target: "dapps", "No NTP servers available. Selecting an older result.");
+				return select_result(last_result.read().1.iter());
+			}
+
+			// Update the results.
 			let mut results = mem::replace(&mut last_result.write().1, VecDeque::new());
+			let has_all_results = results.len() >= MAX_RESULTS;
 			let valid_till = time::Instant::now() + time::Duration::from_secs(
-				if res.is_ok() && results.len() == MAX_RESULTS {
-					UPDATE_TIMEOUT_OK_SECS
-				} else {
-					UPDATE_TIMEOUT_ERR_SECS
+				match res {
+					Ok(time) if has_all_results && time < MAX_DRIFT => UPDATE_TIMEOUT_OK_SECS,
+					Ok(_) if has_all_results => UPDATE_TIMEOUT_WARN_SECS,
+					Err(_) if has_all_results => UPDATE_TIMEOUT_ERR_SECS,
+					_ => UPDATE_TIMEOUT_INCOMPLETE_SECS,
 				}
 			);

+			trace!(target: "dapps", "New time drift received: {:?}", res);
 			// Push the result.
-			results.push_back(res.map(|d| d.num_milliseconds()));
+			results.push_back(res);
 			while results.len() > MAX_RESULTS {
 				results.pop_front();
 			}
@ -209,7 +291,7 @@ mod tests {
 	use std::cell::{Cell, RefCell};
 	use std::time::Instant;
 	use time::Duration;
-	use futures::{self, BoxFuture, Future};
+	use futures::{future, Future};
 	use super::{Ntp, TimeChecker, Error};
 	use util::RwLock;

@ -224,9 +306,11 @@ mod tests {
 	}

 	impl Ntp for FakeNtp {
-		fn drift(&self) -> BoxFuture<Duration, Error> {
+		type Future = future::FutureResult<Duration, Error>;
+
+		fn drift(&self) -> Self::Future {
 			self.1.set(self.1.get() + 1);
-			futures::future::ok(self.0.borrow_mut().pop().expect("Unexpected call to drift().")).boxed()
+			future::ok(self.0.borrow_mut().pop().expect("Unexpected call to drift()."))
 		}
 	}

--- a/dapps/src/lib.rs
+++ b/dapps/src/lib.rs
@ -130,7 +130,7 @@ impl Middleware {

 	/// Creates new middleware for UI server.
 	pub fn ui<F: Fetch>(
-		ntp_server: &str,
+		ntp_servers: &[String],
 		pool: CpuPool,
 		remote: Remote,
 		dapps_domain: &str,
@ -146,7 +146,7 @@ impl Middleware {
 		).embeddable_on(None).allow_dapps(false));
 		let special = {
 			let mut special = special_endpoints(
-				ntp_server,
+				ntp_servers,
 				pool,
 				content_fetcher.clone(),
 				remote.clone(),
@ -171,7 +171,7 @@ impl Middleware {

 	/// Creates new Dapps server middleware.
 	pub fn dapps<F: Fetch>(
-		ntp_server: &str,
+		ntp_servers: &[String],
 		pool: CpuPool,
 		remote: Remote,
 		ui_address: Option<(String, u16)>,
@ -203,7 +203,7 @@ impl Middleware {

 		let special = {
 			let mut special = special_endpoints(
-				ntp_server,
+				ntp_servers,
 				pool,
 				content_fetcher.clone(),
 				remote.clone(),
@ -237,8 +237,8 @@ impl http::RequestMiddleware for Middleware {
 	}
 }

-fn special_endpoints(
-	ntp_server: &str,
+fn special_endpoints<T: AsRef<str>>(
+	ntp_servers: &[T],
 	pool: CpuPool,
 	content_fetcher: Arc<apps::fetcher::Fetcher>,
 	remote: Remote,
@ -250,7 +250,7 @@ fn special_endpoints(
 	special.insert(router::SpecialEndpoint::Api, Some(api::RestApi::new(
 		content_fetcher,
 		sync_status,
-		api::TimeChecker::new(ntp_server.into(), pool),
+		api::TimeChecker::new(ntp_servers, pool),
 		remote,
 	)));
 	special
--- a/dapps/src/tests/helpers/mod.rs
+++ b/dapps/src/tests/helpers/mod.rs
@ -255,7 +255,7 @@ impl Server {
 		fetch: F,
 	) -> Result<Server, http::Error> {
 		let middleware = Middleware::dapps(
-			"pool.ntp.org:123",
+			&["0.pool.ntp.org:123".into(), "1.pool.ntp.org:123".into()],
 			CpuPool::new(4),
 			remote,
 			signer_address,
--- a/parity/cli/config.toml
+++ b/parity/cli/config.toml
@ -78,7 +78,7 @@ disable_periodic = true
 jit = false

 [misc]
-ntp_server = "pool.ntp.org:123"
+ntp_servers = ["0.parity.pool.ntp.org:123"]
 logging = "own_tx=trace"
 log_file = "/var/log/parity.log"
 color = true
--- a/parity/cli/mod.rs
+++ b/parity/cli/mod.rs
@ -359,8 +359,8 @@ usage! {
 			or |c: &Config| otry!(c.vm).jit.clone(),

 		// -- Miscellaneous Options
-		flag_ntp_server: String = "none",
-			or |c: &Config| otry!(c.misc).ntp_server.clone(),
+		flag_ntp_servers: String = "0.parity.pool.ntp.org:123,1.parity.pool.ntp.org:123,2.parity.pool.ntp.org:123,3.parity.pool.ntp.org:123",
+			or |c: &Config| otry!(c.misc).ntp_servers.clone().map(|vec| vec.join(",")),
 		flag_logging: Option<String> = None,
 			or |c: &Config| otry!(c.misc).logging.clone().map(Some),
 		flag_log_file: Option<String> = None,
@ -606,7 +606,7 @@ struct VM {

 #[derive(Default, Debug, PartialEq, Deserialize)]
 struct Misc {
-	ntp_server: Option<String>,
+	ntp_servers: Option<Vec<String>>,
 	logging: Option<String>,
 	log_file: Option<String>,
 	color: Option<bool>,
@ -919,7 +919,7 @@ mod tests {
 			flag_dapps_apis_all: None,

 			// -- Miscellaneous Options
-			flag_ntp_server: "none".into(),
+			flag_ntp_servers: "0.parity.pool.ntp.org:123,1.parity.pool.ntp.org:123,2.parity.pool.ntp.org:123,3.parity.pool.ntp.org:123".into(),
 			flag_version: false,
 			flag_logging: Some("own_tx=trace".into()),
 			flag_log_file: Some("/var/log/parity.log".into()),
@ -1098,7 +1098,7 @@ mod tests {
 				jit: Some(false),
 			}),
 			misc: Some(Misc {
-				ntp_server: Some("pool.ntp.org:123".into()),
+				ntp_servers: Some(vec!["0.parity.pool.ntp.org:123".into()]),
 				logging: Some("own_tx=trace".into()),
 				log_file: Some("/var/log/parity.log".into()),
 				color: Some(true),
--- a/parity/cli/usage.txt
+++ b/parity/cli/usage.txt
@ -483,8 +483,10 @@ Internal Options:
  --can-restart                    Executable will auto-restart if exiting with 69.

 Miscellaneous Options:
-  --ntp-server HOST                NTP server to provide current time (host:port). Used to verify node health.
-                                   (default: {flag_ntp_server})
+  --ntp-servers HOSTS              Comma separated list of NTP servers to provide current time (host:port).
+                                   Used to verify node health. Parity uses pool.ntp.org NTP servers,
+                                   consider joining the pool: http://www.pool.ntp.org/join.html
+                                   (default: {flag_ntp_servers})
  -l --logging LOGGING             Specify the logging level. Must conform to the same
                                   format as RUST_LOG. (default: {flag_logging:?})
  --log-file FILENAME              Specify a filename into which logging should be
--- a/parity/configuration.rs
+++ b/parity/configuration.rs
@ -551,10 +551,14 @@ impl Configuration {
 		Ok(options)
 	}

+	fn ntp_servers(&self) -> Vec<String> {
+		self.args.flag_ntp_servers.split(",").map(str::to_owned).collect()
+	}
+
 	fn ui_config(&self) -> UiConfiguration {
 		UiConfiguration {
 			enabled: self.ui_enabled(),
-			ntp_server: self.args.flag_ntp_server.clone(),
+			ntp_servers: self.ntp_servers(),
 			interface: self.ui_interface(),
 			port: self.args.flag_ports_shift + self.args.flag_ui_port,
 			hosts: self.ui_hosts(),
@ -564,7 +568,7 @@ impl Configuration {
 	fn dapps_config(&self) -> DappsConfiguration {
 		DappsConfiguration {
 			enabled: self.dapps_enabled(),
-			ntp_server: self.args.flag_ntp_server.clone(),
+			ntp_servers: self.ntp_servers(),
 			dapps_path: PathBuf::from(self.directories().dapps),
 			extra_dapps: if self.args.cmd_dapp {
 				self.args.arg_path.iter().map(|path| PathBuf::from(path)).collect()
@ -1278,7 +1282,12 @@ mod tests {
 			support_token_api: true
 		}, UiConfiguration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: vec![
+				"0.parity.pool.ntp.org:123".into(),
+				"1.parity.pool.ntp.org:123".into(),
+				"2.parity.pool.ntp.org:123".into(),
+				"3.parity.pool.ntp.org:123".into(),
+			],
 			interface: "127.0.0.1".into(),
 			port: 8180,
 			hosts: Some(vec![]),
@ -1521,10 +1530,16 @@ mod tests {
 		let conf3 = parse(&["parity", "--ui-path", "signer", "--ui-interface", "test"]);

 		// then
+		let ntp_servers = vec![
+			"0.parity.pool.ntp.org:123".into(),
+			"1.parity.pool.ntp.org:123".into(),
+			"2.parity.pool.ntp.org:123".into(),
+			"3.parity.pool.ntp.org:123".into(),
+		];
 		assert_eq!(conf0.directories().signer, "signer".to_owned());
 		assert_eq!(conf0.ui_config(), UiConfiguration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: ntp_servers.clone(),
 			interface: "127.0.0.1".into(),
 			port: 8180,
 			hosts: Some(vec![]),
@ -1533,7 +1548,7 @@ mod tests {
 		assert_eq!(conf1.directories().signer, "signer".to_owned());
 		assert_eq!(conf1.ui_config(), UiConfiguration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: ntp_servers.clone(),
 			interface: "127.0.0.1".into(),
 			port: 8180,
 			hosts: Some(vec![]),
@ -1543,7 +1558,7 @@ mod tests {
 		assert_eq!(conf2.directories().signer, "signer".to_owned());
 		assert_eq!(conf2.ui_config(), UiConfiguration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: ntp_servers.clone(),
 			interface: "127.0.0.1".into(),
 			port: 3123,
 			hosts: Some(vec![]),
@ -1552,7 +1567,7 @@ mod tests {
 		assert_eq!(conf3.directories().signer, "signer".to_owned());
 		assert_eq!(conf3.ui_config(), UiConfiguration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: ntp_servers.clone(),
 			interface: "test".into(),
 			port: 8180,
 			hosts: Some(vec![]),
--- a/parity/dapps.rs
+++ b/parity/dapps.rs
@ -36,7 +36,7 @@ use util::{Bytes, Address};
 #[derive(Debug, PartialEq, Clone)]
 pub struct Configuration {
 	pub enabled: bool,
-	pub ntp_server: String,
+	pub ntp_servers: Vec<String>,
 	pub dapps_path: PathBuf,
 	pub extra_dapps: Vec<PathBuf>,
 	pub extra_embed_on: Vec<(String, u16)>,
@ -47,7 +47,12 @@ impl Default for Configuration {
 		let data_dir = default_data_path();
 		Configuration {
 			enabled: true,
-			ntp_server: "none".into(),
+			ntp_servers: vec![
+				"0.parity.pool.ntp.org:123".into(),
+				"1.parity.pool.ntp.org:123".into(),
+				"2.parity.pool.ntp.org:123".into(),
+				"3.parity.pool.ntp.org:123".into(),
+			],
 			dapps_path: replace_home(&data_dir, "$BASE/dapps").into(),
 			extra_dapps: vec![],
 			extra_embed_on: vec![],
@ -158,7 +163,7 @@ pub fn new(configuration: Configuration, deps: Dependencies) -> Result<Option<Mi

 	server::dapps_middleware(
 		deps,
-		&configuration.ntp_server,
+		&configuration.ntp_servers,
 		configuration.dapps_path,
 		configuration.extra_dapps,
 		rpc::DAPPS_DOMAIN,
@ -166,14 +171,14 @@ pub fn new(configuration: Configuration, deps: Dependencies) -> Result<Option<Mi
 	).map(Some)
 }

-pub fn new_ui(enabled: bool, ntp_server: &str, deps: Dependencies) -> Result<Option<Middleware>, String> {
+pub fn new_ui(enabled: bool, ntp_servers: &[String], deps: Dependencies) -> Result<Option<Middleware>, String> {
 	if !enabled {
 		return Ok(None);
 	}

 	server::ui_middleware(
 		deps,
-		ntp_server,
+		ntp_servers,
 		rpc::DAPPS_DOMAIN,
 	).map(Some)
 }
@ -204,7 +209,7 @@ mod server {

 	pub fn dapps_middleware(
 		_deps: Dependencies,
-		_ntp_server: &str,
+		_ntp_servers: &[String],
 		_dapps_path: PathBuf,
 		_extra_dapps: Vec<PathBuf>,
 		_dapps_domain: &str,
@ -215,7 +220,7 @@ mod server {

 	pub fn ui_middleware(
 		_deps: Dependencies,
-		_ntp_server: &str,
+		_ntp_servers: &[String],
 		_dapps_domain: &str,
 	) -> Result<Middleware, String> {
 		Err("Your Parity version has been compiled without UI support.".into())
@ -241,7 +246,7 @@ mod server {

 	pub fn dapps_middleware(
 		deps: Dependencies,
-		ntp_server: &str,
+		ntp_servers: &[String],
 		dapps_path: PathBuf,
 		extra_dapps: Vec<PathBuf>,
 		dapps_domain: &str,
@ -252,7 +257,7 @@ mod server {
 		let web_proxy_tokens = Arc::new(move |token| signer.web_proxy_access_token_domain(&token));

 		Ok(parity_dapps::Middleware::dapps(
-			ntp_server,
+			ntp_servers,
 			deps.pool,
 			parity_remote,
 			deps.ui_address,
@ -269,12 +274,12 @@ mod server {

 	pub fn ui_middleware(
 		deps: Dependencies,
-		ntp_server: &str,
+		ntp_servers: &[String],
 		dapps_domain: &str,
 	) -> Result<Middleware, String> {
 		let parity_remote = parity_reactor::Remote::new(deps.remote.clone());
 		Ok(parity_dapps::Middleware::ui(
-			ntp_server,
+			ntp_servers,
 			deps.pool,
 			parity_remote,
 			dapps_domain,
--- a/parity/rpc.rs
+++ b/parity/rpc.rs
@ -73,7 +73,7 @@ impl Default for HttpConfiguration {
 #[derive(Debug, PartialEq, Clone)]
 pub struct UiConfiguration {
 	pub enabled: bool,
-	pub ntp_server: String,
+	pub ntp_servers: Vec<String>,
 	pub interface: String,
 	pub port: u16,
 	pub hosts: Option<Vec<String>>,
@ -107,7 +107,12 @@ impl Default for UiConfiguration {
 	fn default() -> Self {
 		UiConfiguration {
 			enabled: true && cfg!(feature = "ui-enabled"),
-			ntp_server: "none".into(),
+			ntp_servers: vec![
+				"0.parity.pool.ntp.org:123".into(),
+				"1.parity.pool.ntp.org:123".into(),
+				"2.parity.pool.ntp.org:123".into(),
+				"3.parity.pool.ntp.org:123".into(),
+			],
 			port: 8180,
 			interface: "127.0.0.1".into(),
 			hosts: Some(vec![]),
--- a/parity/run.rs
+++ b/parity/run.rs
@ -311,7 +311,7 @@ fn execute_light(cmd: RunCmd, can_restart: bool, logger: Arc<RotatingLogger>) ->
 	};

 	let dapps_middleware = dapps::new(cmd.dapps_conf.clone(), dapps_deps.clone())?;
-	let ui_middleware = dapps::new_ui(cmd.ui_conf.enabled, &cmd.ui_conf.ntp_server, dapps_deps)?;
+	let ui_middleware = dapps::new_ui(cmd.ui_conf.enabled, &cmd.ui_conf.ntp_servers, dapps_deps)?;

 	// start RPCs
 	let dapps_service = dapps::service(&dapps_middleware);
@ -687,7 +687,7 @@ pub fn execute(cmd: RunCmd, can_restart: bool, logger: Arc<RotatingLogger>) -> R
 		}
 	};
 	let dapps_middleware = dapps::new(cmd.dapps_conf.clone(), dapps_deps.clone())?;
-	let ui_middleware = dapps::new_ui(cmd.ui_conf.enabled, &cmd.ui_conf.ntp_server, dapps_deps)?;
+	let ui_middleware = dapps::new_ui(cmd.ui_conf.enabled, &cmd.ui_conf.ntp_servers, dapps_deps)?;

 	let dapps_service = dapps::service(&dapps_middleware);
 	let deps_for_rpc_apis = Arc::new(rpc_apis::FullDependencies {