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Add jitter to LazyCredentialsCache #2335

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merged 3 commits into from
Feb 10, 2023
Merged

Add jitter to LazyCredentialsCache #2335

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99a905c
Add jitter to `LazyCredentialsCache`
ysaito1001 Feb 8, 2023
26c782f
Update CHANGELOG.next.toml
ysaito1001 Feb 8, 2023
f2d98bc
Merge branch 'main' into ysaito/add-jitter-to-lazy-cache
ysaito1001 Feb 10, 2023
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6 changes: 6 additions & 0 deletions CHANGELOG.next.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,3 +10,9 @@
# references = ["smithy-rs#920"]
# meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "client | server | all"}
# author = "rcoh"

[[aws-sdk-rust]]
message = "Adds jitter to `LazyCredentialsCache`. This allows credentials with the same expiry to expire at slightly different times, thereby preventing thundering herds."
references = ["smithy-rs#2335"]
meta = { "breaking" = false, "tada" = false, "bug" = false }
author = "ysaito1001"
1 change: 1 addition & 0 deletions aws/rust-runtime/aws-credential-types/Cargo.toml
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Expand Up @@ -14,6 +14,7 @@ test-util = []
[dependencies]
aws-smithy-async = { path = "../../../rust-runtime/aws-smithy-async" }
aws-smithy-types = { path = "../../../rust-runtime/aws-smithy-types" }
fastrand = "1.4.0"
tokio = { version = "1.8.4", features = ["sync"] }
tracing = "0.1"
zeroize = "1"
Expand Down
97 changes: 89 additions & 8 deletions aws/rust-runtime/aws-credential-types/src/cache/lazy_caching.rs
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Expand Up @@ -20,6 +20,7 @@ use crate::time_source::TimeSource;
const DEFAULT_LOAD_TIMEOUT: Duration = Duration::from_secs(5);
const DEFAULT_CREDENTIAL_EXPIRATION: Duration = Duration::from_secs(15 * 60);
const DEFAULT_BUFFER_TIME: Duration = Duration::from_secs(10);
const DEFAULT_BUFFER_TIME_JITTER_FRACTION: fn() -> f64 = fastrand::f64;

#[derive(Debug)]
pub(crate) struct LazyCredentialsCache {
Expand All @@ -28,6 +29,8 @@ pub(crate) struct LazyCredentialsCache {
cache: ExpiringCache<Credentials, CredentialsError>,
provider: SharedCredentialsProvider,
load_timeout: Duration,
buffer_time: Duration,
buffer_time_jitter_fraction: fn() -> f64,
default_credential_expiration: Duration,
}

Expand All @@ -37,15 +40,18 @@ impl LazyCredentialsCache {
sleeper: Arc<dyn AsyncSleep>,
provider: SharedCredentialsProvider,
load_timeout: Duration,
default_credential_expiration: Duration,
buffer_time: Duration,
buffer_time_jitter_fraction: fn() -> f64,
default_credential_expiration: Duration,
) -> Self {
Self {
time,
sleeper,
cache: ExpiringCache::new(buffer_time),
provider,
load_timeout,
buffer_time,
buffer_time_jitter_fraction,
default_credential_expiration,
}
}
Expand Down Expand Up @@ -95,7 +101,12 @@ impl ProvideCachedCredentials for LazyCredentialsCache {
let expiry = credentials
.expiry()
.unwrap_or(now + default_credential_expiration);
Ok((credentials, expiry))

let jitter = self
.buffer_time
.mul_f64((self.buffer_time_jitter_fraction)());

Ok((credentials, expiry + jitter))
}
// Only instrument the the actual load future so that no span
// is opened if the cache decides not to execute it.
Expand Down Expand Up @@ -125,8 +136,8 @@ mod builder {

use super::TimeSource;
use super::{
LazyCredentialsCache, DEFAULT_BUFFER_TIME, DEFAULT_CREDENTIAL_EXPIRATION,
DEFAULT_LOAD_TIMEOUT,
LazyCredentialsCache, DEFAULT_BUFFER_TIME, DEFAULT_BUFFER_TIME_JITTER_FRACTION,
DEFAULT_CREDENTIAL_EXPIRATION, DEFAULT_LOAD_TIMEOUT,
};

/// Builder for constructing a `LazyCredentialsCache`.
Expand All @@ -147,6 +158,7 @@ mod builder {
time_source: Option<TimeSource>,
load_timeout: Option<Duration>,
buffer_time: Option<Duration>,
buffer_time_jitter_fraction: Option<fn() -> f64>,
default_credential_expiration: Option<Duration>,
}

Expand Down Expand Up @@ -228,6 +240,38 @@ mod builder {
self
}

/// A random percentage by which buffer time is jittered for randomization.
///
/// For example, if credentials are expiring in 15 minutes, the buffer time is 10 seconds,
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It seems like the Go V2 jitter applies to the whole expiration window rather than to the buffer time. What is your reasoning for applying it to the 10 second buffer time?

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Go V2's term ExpiryWindow actually means the buffer time in the Rust SDK.

ExpiryWindow will allow the credentials to trigger refreshing prior to the credentials actually expiring.

In our case, ExpiringCache automatically takes care of buffer time, specifically within the expired function.

/// and buffer time jitter fraction is 0.2, then buffer time is adjusted to 8 seconds.
/// Therefore, any requests made after 14 minutes and 52 seconds will load new credentials.
///
/// Defaults to a randomly generated value between 0.0 and 1.0. This setter is for testing only.
#[cfg(feature = "test-util")]
pub fn buffer_time_jitter_fraction(
mut self,
buffer_time_jitter_fraction: fn() -> f64,
) -> Self {
self.set_buffer_time_jitter_fraction(Some(buffer_time_jitter_fraction));
self
}

/// A random percentage by which buffer time is jittered for randomization.
///
/// For example, if credentials are expiring in 15 minutes, the buffer time is 10 seconds,
/// and buffer time jitter fraction is 0.2, then buffer time is adjusted to 8 seconds.
/// Therefore, any requests made after 14 minutes and 52 seconds will load new credentials.
///
/// Defaults to a randomly generated value between 0.0 and 1.0. This setter is for testing only.
#[cfg(feature = "test-util")]
pub fn set_buffer_time_jitter_fraction(
&mut self,
buffer_time_jitter_fraction: Option<fn() -> f64>,
) -> &mut Self {
self.buffer_time_jitter_fraction = buffer_time_jitter_fraction;
self
}

/// Default expiration time to set on credentials if they don't have an expiration time.
///
/// This is only used if the given [`ProvideCredentials`](crate::provider::ProvideCredentials) returns
Expand Down Expand Up @@ -283,8 +327,10 @@ mod builder {
}),
provider,
self.load_timeout.unwrap_or(DEFAULT_LOAD_TIMEOUT),
default_credential_expiration,
self.buffer_time.unwrap_or(DEFAULT_BUFFER_TIME),
self.buffer_time_jitter_fraction
.unwrap_or(DEFAULT_BUFFER_TIME_JITTER_FRACTION),
default_credential_expiration,
)
}
}
Expand All @@ -310,8 +356,11 @@ mod tests {
DEFAULT_LOAD_TIMEOUT,
};

const BUFFER_TIME_NO_JITTER: fn() -> f64 = || 0_f64;

fn test_provider(
time: TimeSource,
buffer_time_jitter_fraction: fn() -> f64,
load_list: Vec<crate::provider::Result>,
) -> LazyCredentialsCache {
let load_list = Arc::new(Mutex::new(load_list));
Expand All @@ -327,8 +376,9 @@ mod tests {
}
})),
DEFAULT_LOAD_TIMEOUT,
DEFAULT_CREDENTIAL_EXPIRATION,
DEFAULT_BUFFER_TIME,
buffer_time_jitter_fraction,
DEFAULT_CREDENTIAL_EXPIRATION,
)
}

Expand Down Expand Up @@ -361,8 +411,9 @@ mod tests {
Arc::new(TokioSleep::new()),
provider,
DEFAULT_LOAD_TIMEOUT,
DEFAULT_CREDENTIAL_EXPIRATION,
DEFAULT_BUFFER_TIME,
BUFFER_TIME_NO_JITTER,
DEFAULT_CREDENTIAL_EXPIRATION,
);
assert_eq!(
epoch_secs(1000),
Expand All @@ -381,6 +432,7 @@ mod tests {
let mut time = TestingTimeSource::new(epoch_secs(100));
let credentials_cache = test_provider(
TimeSource::testing(&time),
BUFFER_TIME_NO_JITTER,
vec![
Ok(credentials(1000)),
Ok(credentials(2000)),
Expand All @@ -404,6 +456,7 @@ mod tests {
let mut time = TestingTimeSource::new(epoch_secs(100));
let credentials_cache = test_provider(
TimeSource::testing(&time),
BUFFER_TIME_NO_JITTER,
vec![
Ok(credentials(1000)),
Err(CredentialsError::not_loaded("failed")),
Expand All @@ -430,6 +483,7 @@ mod tests {
let time = TestingTimeSource::new(epoch_secs(0));
let credentials_cache = Arc::new(test_provider(
TimeSource::testing(&time),
BUFFER_TIME_NO_JITTER,
vec![
Ok(credentials(500)),
Ok(credentials(1500)),
Expand Down Expand Up @@ -480,13 +534,40 @@ mod tests {
Ok(credentials(1000))
})),
Duration::from_millis(5),
DEFAULT_CREDENTIAL_EXPIRATION,
DEFAULT_BUFFER_TIME,
BUFFER_TIME_NO_JITTER,
DEFAULT_CREDENTIAL_EXPIRATION,
);

assert!(matches!(
credentials_cache.provide_cached_credentials().await,
Err(CredentialsError::ProviderTimedOut { .. })
));
}

#[tokio::test]
async fn buffer_time_jitter() {
let mut time = TestingTimeSource::new(epoch_secs(100));
let buffer_time_jitter_fraction = || 0.5_f64;
let credentials_cache = test_provider(
TimeSource::testing(&time),
buffer_time_jitter_fraction,
vec![Ok(credentials(1000)), Ok(credentials(2000))],
);

expect_creds(1000, &credentials_cache).await;
let buffer_time_with_jitter =
(DEFAULT_BUFFER_TIME.as_secs_f64() * buffer_time_jitter_fraction()) as u64;
assert_eq!(buffer_time_with_jitter, 5);
// Advance time to the point where the first credentials are about to expire (but haven't).
let almost_expired_secs = 1000 - buffer_time_with_jitter - 1;
time.set_time(epoch_secs(almost_expired_secs));
// We should still use the first credentials.
expect_creds(1000, &credentials_cache).await;
// Now let the first credentials expire.
let expired_secs = almost_expired_secs + 1;
time.set_time(epoch_secs(expired_secs));
// Now that the first credentials have been expired, the second credentials will be retrieved.
expect_creds(2000, &credentials_cache).await;
}
}