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[adapters] NATS: Fix "consumer already exists" error for named consumers #5526

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Merged
blp merged 3 commits into from
Jan 29, 2026
Merged

[adapters] NATS: Fix "consumer already exists" error for named consumers #5526

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a26c232
[adapters] NATS: Add test for named consumer during restart/replay
kfollesdal Jan 28, 2026
71fccf8
[adapters] NATS: Fix for named consumer bug
kfollesdal Jan 28, 2026
1b94bba
[adapters] NATS: Add more error context for create consumer
kfollesdal Jan 28, 2026
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21 changes: 18 additions & 3 deletions crates/adapters/src/transport/nats/input.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -322,9 +322,24 @@ async fn create_nats_consumer(
};
}

Ok(jetstream
.create_consumer_strict_on_stream(consumer_config, stream_name)
.await?)
// Add a unique suffix to named consumers.
// If consumer is unnamed, NATS automatically generates a random name.
//
// This fixes "consumer already exists" errors that occurred with rapid
// pipeline restarts/replays before the previous consumer expires (inactive_threshold).
consumer_config.name = consumer_config
.name
.map(|n| format!("{n}_{}", uuid::Uuid::now_v7()));

jetstream
.create_consumer_strict_on_stream(consumer_config.clone(), stream_name)
.await
.with_context(|| {
format!(
"Failed to create consumer {:?} on stream '{}'",
consumer_config.name, stream_name
)
})
}

async fn consume_nats_messages_until(
Expand Down
48 changes: 47 additions & 1 deletion crates/adapters/src/transport/nats/input/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -137,7 +137,30 @@ impl NatsFtTestRound {
}
}

struct NatsFtTestConfig<'a> {
rounds: &'a [NatsFtTestRound],
consumer_name: Option<&'a str>,
}

impl<'a> NatsFtTestConfig<'a> {
fn new(rounds: &'a [NatsFtTestRound]) -> Self {
Self {
rounds,
consumer_name: None,
}
}

fn with_consumer_name(mut self, name: Option<&'a str>) -> Self {
self.consumer_name = name;
self
}
}

fn test_nats_ft(rounds: &[NatsFtTestRound]) {
test_nats_ft_with_config(NatsFtTestConfig::new(rounds));
}

fn test_nats_ft_with_config(test_config: NatsFtTestConfig<'_>) {
init_test_logger();

let (_nats_process_guard, nats_url) = util::start_nats_and_get_address().unwrap();
Expand Down Expand Up @@ -169,6 +192,11 @@ fn test_nats_ft(rounds: &[NatsFtTestRound]) {
create_dir(&storage_dir).unwrap();
let output_path = tempdir_path.join("output.csv");

let consumer_name_line = test_config
.consumer_name
.map(|n| format!("name: {n}"))
.unwrap_or_default();

let config_str = format!(
r#"
name: test
Expand All @@ -188,6 +216,7 @@ inputs:
server_url: {nats_url}
stream_name: {stream_name}
consumer_config:
{consumer_name_line}
deliver_policy: All
subjects: [{subject_name}]
format:
Expand Down Expand Up @@ -217,7 +246,7 @@ outputs:
n_records,
do_checkpoint,
},
) in rounds.iter().cloned().enumerate()
) in test_config.rounds.iter().cloned().enumerate()
{
println!(
"--- round {round}: add {n_records} records, {} ---",
Expand Down Expand Up @@ -443,6 +472,23 @@ fn test_nats_ft_empty_step_checkpoint() {
]);
}

/// Tests rapid restart+replay with a named consumer.
///
/// This reproduces a bug where the previous ordered consumer hadn't expired yet,
/// causing "consumer already exists" errors. The fix generates unique consumer names
/// by appending a UUID suffix when a name is explicitly configured.
#[test]
fn test_nats_ft_with_named_consumer() {
test_nats_ft_with_config(
NatsFtTestConfig::new(&[
NatsFtTestRound::with_checkpoint(5),
NatsFtTestRound::with_checkpoint(5),
NatsFtTestRound::with_checkpoint(0),
])
.with_consumer_name(Some("my_named_consumer")),
);
}

mod util {
use crate::test::wait;
use anyhow::{Result as AnyResult, anyhow};
Expand Down