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RPC Resolver: If all are unhealthy, return the default RPC #77

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Merged
Garandor merged 4 commits into from
Jan 22, 2026
Merged

RPC Resolver: If all are unhealthy, return the default RPC #77

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6acaeac
If all are unhealthy, return the default RPC
Garandor Jan 15, 2026
c447f1c
Initialize RPCs as Unhealthy
Garandor Jan 15, 2026
825fc16
fmt
Garandor Jan 15, 2026
a9c2cfa
cleanup unused code
Garandor Jan 15, 2026
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100 changes: 61 additions & 39 deletions rust/lit-core/lit-blockchain/src/resolver/rpc/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, OnceLock};
use std::time::Duration;
use std::time::SystemTime;
use tracing::trace;
use tracing::{error, trace, warn};
use url::Url;

use ethers::prelude::*;
Expand Down Expand Up @@ -43,8 +43,9 @@ pub struct StandardRpcHealthcheckPoller<'a> {

/// Select the best RPC entry from a non-empty list.
/// Order: healthy > higher priority > lower latency > lexicographically smaller URL.
/// Entries missing in `latencies` are treated as unhealthy; if none are healthy, fall back to
/// highest priority.
/// Entries missing in `latencies` are treated as unhealthy; if none are healthy, fall back to the
/// lexicographically smallest URL among default-priority (0) entries.
/// If that also doesn't exist, print error and return the first entry.
///
/// # Panics
/// Panics if `entries` is empty. Callers must ensure the list is non-empty.
Expand Down Expand Up @@ -73,14 +74,23 @@ fn select_rpc_entry<'a>(
return entry;
}

// No healthy entries - fall back to highest priority regardless of health.
// Uses same comparator pattern as healthy path for consistency and readability.
entries
.iter()
.min_by(|a, b| {
Reverse(a.priority()).cmp(&Reverse(b.priority())).then_with(|| a.url().cmp(b.url()))
})
.expect("entries is non-empty")
// No healthy entries. This happens when the healthcheck poller has not completed a cycle but the
// contract resolver immediately needs an RPC (e.g. prov bootstrap). In that case, all entries are
// default-unhealthy due to missing latency data. We must avoid picking a high-priority replica
// that may not exist; instead use the default-priority remote RPC that is most likely to be
// available and warn that fallback was used. This makes a priority-0 default entry mandatory
// for every chain that may be used during initialization (yellowstone, litChain)
let fallback_entry =
entries.iter().filter(|entry| entry.priority() == 0).min_by(|a, b| a.url().cmp(b.url()));

if let Some(entry) = fallback_entry {
warn!(url = entry.url(), "RPC healthcheck fallback URL selected");
return entry;
}

let entry = entries.first().expect("entries is non-empty");
error!(url = entry.url(), "No default priority RPC provided; falling back to first entry");
entry
}

impl<'a> StandardRpcHealthcheckPoller<'a> {
Expand Down Expand Up @@ -318,11 +328,8 @@ pub trait RpcHealthcheckPoller: Sync {
ArcSwap::from(Arc::new({
let resolver = rpc_resolver.load();
let chains = resolver.config.chains();
let key_values = chains
.values()
.flat_map(|v| v.iter().rev())
.zip((0..).map(|t| Duration::MAX.saturating_sub(Duration::from_secs(t))))
.map(|(k, v)| (k.clone(), Latency::Healthy(v)));
let key_values =
chains.values().flat_map(|v| v.iter()).map(|k| (k.clone(), Latency::Unhealthy));
let mut m = im::hashmap::HashMap::new();
m.extend(key_values);
m
Expand Down Expand Up @@ -417,13 +424,9 @@ impl RpcResolver {
config.chains().values().flat_map(|v| v.iter()).collect();

latencies.retain(|e, _| rpc_entries.contains(e));
for (d, rpc_entry) in config.chains().values().flat_map(|v| {
v.iter().enumerate().rev().map(|(i, v)| {
(Duration::MAX.saturating_sub(Duration::from_secs(164 + i as u64)), v)
})
}) {
for rpc_entry in config.chains().values().flat_map(|v| v.iter()) {
if !latencies.contains_key(rpc_entry) {
latencies.insert(rpc_entry.clone(), Latency::Healthy(d));
latencies.insert(rpc_entry.clone(), Latency::Unhealthy);
}
}

Expand Down Expand Up @@ -752,19 +755,22 @@ mod tests {
}

#[test]
fn test_select_rpc_entry_falls_back_to_priority_when_none_healthy() {
let e_prio_1 =
RpcEntry::new(RpcKind::EVM, "https://p1".into(), None, None).with_priority(1);
let e_prio_2 =
RpcEntry::new(RpcKind::EVM, "https://p2".into(), None, None).with_priority(2);
fn test_select_rpc_entry_falls_back_to_default_priority_when_none_healthy() {
let e_default_zeta =
RpcEntry::new(RpcKind::EVM, "https://zeta".into(), None, None).with_priority(0);
let e_default_alpha =
RpcEntry::new(RpcKind::EVM, "https://alpha".into(), None, None).with_priority(0);
let e_high_prio =
RpcEntry::new(RpcKind::EVM, "https://high".into(), None, None).with_priority(10);

let entries = vec![e_prio_1.clone(), e_prio_2.clone()];
let entries = vec![e_default_zeta.clone(), e_high_prio.clone(), e_default_alpha.clone()];
let mut latencies = im::hashmap::HashMap::new();
latencies.insert(e_prio_1.clone(), Latency::Unhealthy);
latencies.insert(e_prio_2.clone(), Latency::Unhealthy);
latencies.insert(e_default_zeta.clone(), Latency::Unhealthy);
latencies.insert(e_default_alpha.clone(), Latency::Unhealthy);
latencies.insert(e_high_prio.clone(), Latency::Unhealthy);

let selected = select_rpc_entry(&entries, &latencies);
assert_eq!(selected.url(), e_prio_2.url());
assert_eq!(selected.url(), e_default_alpha.url());
}

#[test]
Expand All @@ -783,17 +789,33 @@ mod tests {
}

#[test]
fn test_select_rpc_entry_unknown_entries_fallback_respects_priority() {
let e_low_prio =
RpcEntry::new(RpcKind::EVM, "https://low".into(), None, None).with_priority(1);
fn test_select_rpc_entry_unknown_entries_fallback_prefers_default_priority() {
let e_default_beta =
RpcEntry::new(RpcKind::EVM, "https://beta".into(), None, None).with_priority(0);
let e_default_alpha =
RpcEntry::new(RpcKind::EVM, "https://alpha".into(), None, None).with_priority(0);
let e_high_prio =
RpcEntry::new(RpcKind::EVM, "https://high".into(), None, None).with_priority(10);

let entries = vec![e_low_prio.clone(), e_high_prio.clone()];
let entries = vec![e_default_beta.clone(), e_high_prio.clone(), e_default_alpha.clone()];
let latencies = im::hashmap::HashMap::new();

let selected = select_rpc_entry(&entries, &latencies);
assert_eq!(selected.url(), e_high_prio.url());
assert_eq!(selected.url(), e_default_alpha.url());
}

#[test]
fn test_select_rpc_entry_fallback_uses_first_when_no_default_priority() {
let e_first =
RpcEntry::new(RpcKind::EVM, "https://first".into(), None, None).with_priority(5);
let e_second =
RpcEntry::new(RpcKind::EVM, "https://second".into(), None, None).with_priority(10);

let entries = vec![e_first.clone(), e_second.clone()];
let latencies = im::hashmap::HashMap::new();

let selected = select_rpc_entry(&entries, &latencies);
assert_eq!(selected.url(), e_first.url());
}

#[test]
Expand Down Expand Up @@ -822,9 +844,9 @@ mod tests {
#[test]
fn test_select_rpc_entry_url_tiebreaker_in_fallback_path() {
let e_alpha = RpcEntry::new(RpcKind::EVM, "https://alpha.example.com".into(), None, None)
.with_priority(5);
.with_priority(0);
let e_zeta = RpcEntry::new(RpcKind::EVM, "https://zeta.example.com".into(), None, None)
.with_priority(5);
.with_priority(0);

for entries in
[vec![e_alpha.clone(), e_zeta.clone()], vec![e_zeta.clone(), e_alpha.clone()]]
Expand All @@ -837,7 +859,7 @@ mod tests {
assert_eq!(
selected.url(),
e_alpha.url(),
"Fallback path should use same URL tie-breaking as healthy path"
"Fallback path should use lexicographically smallest default URL"
);
}
}
Expand Down