add support for variable cache expiration jitter

Cargo.toml

@@ -22,6 +22,7 @@ httpdate = "1.0.2"
 log = "0.4.16"
 magick_rust = { git = "https://github.com/nlfiedler/magick-rust", branch = "master", features = ["disable-hdri"] }
 openssl = "0.10.38"
+rand = "0.8.5"
 serde = { version = "1.0.136", features = ["derive"] }
 url = "2.2.2"
 

README.md

@@ -54,15 +54,16 @@ curl localhost:8080/resize?source=image.jpeg&height=100&width=100&quality=85
 
 The Rusty Resizer accepts all its configuration options through ENV variables:
 
-| ENV var                  | description                                                                       | default    |
-| ------------------------ | --------------------------------------------------------------------------------- | ---------- |
-| `ALLOWED_HOSTS`          | **required** list of image hosts that will be accepted for resizing               |            |
-| `DEFAULT_QUALITY`        | default compression quality for image formats that accept compression (e.g. jpeg) | 85         |
-| `CACHE_EXPIRATION_HOURS` | used to populate the Cache-Control max-age headers in the final resized response  | 2880 hours |
-| `STATSD_HOST`            | StatsD host to accept metric data (metrics are only emitted when this is present) |            |
-| `WORKERS`                | number of HTTP workers                                                            | 4          |
-| `PORT`                   | TCP port to bind the server                                                       | 8080       |
-| `ENV`                    | environment the server is running in                                              | local      |
+| ENV var                  | description                                                                            | default    |
+| ------------------------ | -------------------------------------------------------------------------------------- | ---------- |
+| `ALLOWED_HOSTS`          | **required** list of image hosts that will be accepted for resizing                    |            |
+| `DEFAULT_QUALITY`        | default compression quality for image formats that accept compression (e.g. jpeg)      | 85         |
+| `CACHE_EXPIRATION_HOURS` | use to populate `Cache-Control` & `Expires` headers in the final resized response      | 2880 hours |
+| `CACHE_JITTER_SECONDS`   | help give `Cache-Control` & `Expires` headers some variance to avoid a thundering herd | 0          |
+| `STATSD_HOST`            | StatsD host to accept metric data (metrics are only emitted when this is present)      |            |
+| `WORKERS`                | number of HTTP workers                                                                 | 4          |
+| `PORT`                   | TCP port to bind the server                                                            | 8080       |
+| `ENV`                    | environment the server is running in                                                   | local      |
 
 ## Security
 

src/lib.rs

@@ -10,6 +10,7 @@ use futures_util::future::FutureExt;
 use http::Client;
 use img::{Image, ImageError};
 use magick_rust::magick_wand_genesis;
+use rand::Rng;
 use serde::Deserialize;
 use std::net::TcpListener;
 use std::sync::{Arc, Once};
@@ -26,6 +27,7 @@ pub struct Configuration {
     pub env: String,
     pub allowed_hosts: Vec<Host>,
     pub cache_expiration: u64,
+    pub cache_jitter: u64,
     pub default_quality: u8,
 }
 
@@ -36,17 +38,19 @@ impl Configuration {
     /// # use url::Host;
     /// # use rusty_resizer::Configuration;
     ///
-    /// let config = Configuration::new(String::from("test"), String::from("  x.com,  y.com,z.com"), 2880, 50);
+    /// let config = Configuration::new(String::from("test"), String::from("  x.com,  y.com,z.com"), 2880, 60, 50);
     ///
     /// assert_eq!("test", config.env);
     /// assert_eq!(vec![Host::parse("x.com").unwrap(), Host::parse("y.com").unwrap(), Host::parse("z.com").unwrap()], config.allowed_hosts);
     /// assert_eq!(2880, config.cache_expiration);
+    /// assert_eq!(60, config.cache_jitter);
     /// assert_eq!(50, config.default_quality);
     /// ```
     pub fn new(
         env: String,
         allowed_hosts: String,
         cache_expiration: u64,
+        cache_jitter: u64,
         default_quality: u8,
     ) -> Self {
         let allowed_hosts = allowed_hosts
@@ -62,6 +66,7 @@ impl Configuration {
             env,
             allowed_hosts,
             cache_expiration,
+            cache_jitter,
             default_quality,
         }
     }
@@ -109,7 +114,12 @@ async fn resize(
             let content_type = image.mime_type()?;
 
             let now = SystemTime::now();
-            let expire_time_in_seconds = configuration.cache_expiration * 60 * 60;
+            let jitter = if configuration.cache_jitter > 0 {
+                rand::thread_rng().gen_range(0..configuration.cache_jitter)
+            } else {
+                0
+            };
+            let expire_time_in_seconds = configuration.cache_expiration * 60 * 60 + jitter;
 
             let response = HttpResponse::Ok()
                 .content_type(content_type)

src/main.rs

@@ -7,6 +7,7 @@ use std::net::UdpSocket;
 const DEFAULT_WORKERS: usize = 4;
 const DEFAULT_QUALITY: u8 = 85;
 const DEFAULT_CACHE_EXPIRATION_HOURS: u64 = 2880;
+const DEFAULT_CACHE_JITTER_SECONDS: u64 = 0;
 
 #[actix_web::main]
 async fn main() -> std::io::Result<()> {
@@ -26,12 +27,22 @@ async fn main() -> std::io::Result<()> {
         .ok()
         .and_then(|ce| ce.parse::<u64>().ok())
         .unwrap_or(DEFAULT_CACHE_EXPIRATION_HOURS);
+    let cache_jitter = env::var("CACHE_JITTER_SECONDS")
+        .ok()
+        .and_then(|ce| ce.parse::<u64>().ok())
+        .unwrap_or(DEFAULT_CACHE_JITTER_SECONDS);
     let statsd_host = env::var("STATSD_HOST").ok();
     // App Configuration
     let address = format!("0.0.0.0:{}", port);
     let listener =
         TcpListener::bind(address).unwrap_or_else(|_| panic!("Failed to bind to port {}!", port));
-    let configuration = Configuration::new(env, allowed_hosts, cache_expiration, default_quality);
+    let configuration = Configuration::new(
+        env,
+        allowed_hosts,
+        cache_expiration,
+        cache_jitter,
+        default_quality,
+    );
     // Logging
     use env_logger;
     env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));

tests/support/mod.rs

@@ -11,6 +11,7 @@ pub fn spawn_app() -> String {
         env: String::from("test"),
         allowed_hosts: vec![Host::parse("raw.githubusercontent.com").unwrap()],
         cache_expiration: 1,
+        cache_jitter: 0,
         default_quality: 85,
     };
     let statsd = StatsdClient::from_sink("rusty.resizer", NopMetricSink);