feat(config): Allow environment references in Relay configuration (#4748)

Allow `${VAR}` references in Relay's config. Any leaf value can now be a
reference to an environment variable.

Fixes: #4647

Author: Dav1dde

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+**Features**:
+
+- Allow environment references in Relay configuration. ([#4748](https://github.com/getsentry/relay/pull/4748))
+
 ## 25.5.0
 
 **Features**:

Cargo.lock

@@ -172,6 +172,7 @@ sentry-types = "0.36.0"
 sentry_protos = "0.2.0"
 serde = { version = "1.0.215", features = ["derive", "rc"] }
 serde-transcode = "1.1.1"
+serde-vars = "0.1"
 serde_bytes = "0.11"
 serde_json = "1.0.133"
 serde_path_to_error = "0.1.16"

Cargo.toml

@@ -27,6 +27,7 @@ relay-log = { workspace = true, features = ["init"] }
 relay-metrics = { workspace = true }
 relay-redis = { workspace = true }
 serde = { workspace = true }
+serde-vars = { workspace = true }
 serde_json = { workspace = true }
 serde_yaml = { workspace = true }
 thiserror = { workspace = true }

relay-config/Cargo.toml

@@ -174,12 +174,18 @@ trait ConfigObject: DeserializeOwned + Serialize {
 
         let f = fs::File::open(&path)
             .with_context(|| ConfigError::file(ConfigErrorKind::CouldNotOpenFile, &path))?;
+        let f = io::BufReader::new(f);
 
+        let mut source = serde_vars::EnvSource::default();
         match Self::format() {
-            ConfigFormat::Yaml => serde_yaml::from_reader(io::BufReader::new(f))
-                .with_context(|| ConfigError::file(ConfigErrorKind::BadYaml, &path)),
-            ConfigFormat::Json => serde_json::from_reader(io::BufReader::new(f))
-                .with_context(|| ConfigError::file(ConfigErrorKind::BadJson, &path)),
+            ConfigFormat::Yaml => {
+                serde_vars::deserialize(serde_yaml::Deserializer::from_reader(f), &mut source)
+                    .with_context(|| ConfigError::file(ConfigErrorKind::BadYaml, &path))
+            }
+            ConfigFormat::Json => {
+                serde_vars::deserialize(&mut serde_json::Deserializer::from_reader(f), &mut source)
+                    .with_context(|| ConfigError::file(ConfigErrorKind::BadJson, &path))
+            }
         }
     }
 

relay-config/src/config.rs

@@ -28,3 +28,19 @@ def test_invalid_topics_raise_error(mini_sentry, relay_with_processing):
 
     error = str(mini_sentry.test_failures.get_nowait())
     assert "failed to validate the topic with name" in error
+
+
+def test_missing_env_var_in_config(mini_sentry, relay, relay_credentials):
+    credentials = relay_credentials()
+    relay = relay(
+        mini_sentry,
+        credentials=credentials,
+        wait_health_check=False,
+        options={
+            "http": {
+                "encoding": "${THIS_DOES_NOT_EXIST_OTHER_WISE_THE_TEST_WILL_PASS}",
+            }
+        },
+    )
+
+    assert relay.wait_for_exit() != 0