fix(pageserver): make posthog config parsing more robust (#12356)

## Problem

In our infra config, we have to split server_api_key and other fields in
two files: the former one in the sops file, and the latter one in the
normal config. It creates the situation that we might misconfigure some
regions that it only has part of the fields available, causing
storcon/pageserver refuse to start.

## Summary of changes

Allow PostHog config to have part of the fields available. Parse it
later.

Signed-off-by: Alex Chi Z <chi@neon.tech>

pageserver/src/config.rs

@@ -781,4 +781,21 @@ mod tests {
         PageServerConf::parse_and_validate(NodeId(0), config_toml, &workdir)
             .expect("parse_and_validate");
     }
+
+    #[test]
+    fn test_config_posthog_incomplete_config_is_valid() {
+        let input = r#"
+            control_plane_api = "http://localhost:6666"
+
+            [posthog_config]
+            server_api_key = "phs_AAA"
+            private_api_url = "https://us.posthog.com"
+            public_api_url = "https://us.i.posthog.com"
+        "#;
+        let config_toml = toml_edit::de::from_str::<pageserver_api::config::ConfigToml>(input)
+            .expect("posthogconfig is valid");
+        let workdir = Utf8PathBuf::from("/nonexistent");
+        PageServerConf::parse_and_validate(NodeId(0), config_toml, &workdir)
+            .expect("parse_and_validate");
+    }
 }

pageserver/src/feature_resolver.rs

@@ -3,7 +3,7 @@ use std::{collections::HashMap, sync::Arc, time::Duration};
 use arc_swap::ArcSwap;
 use pageserver_api::config::NodeMetadata;
 use posthog_client_lite::{
-    CaptureEvent, FeatureResolverBackgroundLoop, PostHogClientConfig, PostHogEvaluationError,
+    CaptureEvent, FeatureResolverBackgroundLoop, PostHogEvaluationError,
     PostHogFlagFilterPropertyValue,
 };
 use remote_storage::RemoteStorageKind;
@@ -45,16 +45,24 @@ impl FeatureResolver {
     ) -> anyhow::Result<Self> {
         // DO NOT block in this function: make it return as fast as possible to avoid startup delays.
         if let Some(posthog_config) = &conf.posthog_config {
-            let inner = FeatureResolverBackgroundLoop::new(
-                PostHogClientConfig {
-                    server_api_key: posthog_config.server_api_key.clone(),
-                    client_api_key: posthog_config.client_api_key.clone(),
-                    project_id: posthog_config.project_id.clone(),
-                    private_api_url: posthog_config.private_api_url.clone(),
-                    public_api_url: posthog_config.public_api_url.clone(),
-                },
-                shutdown_pageserver,
-            );
+            let posthog_client_config = match posthog_config.clone().try_into_posthog_config() {
+                Ok(config) => config,
+                Err(e) => {
+                    tracing::warn!(
+                        "invalid posthog config, skipping posthog integration: {}",
+                        e
+                    );
+                    return Ok(FeatureResolver {
+                        inner: None,
+                        internal_properties: None,
+                        force_overrides_for_testing: Arc::new(ArcSwap::new(Arc::new(
+                            HashMap::new(),
+                        ))),
+                    });
+                }
+            };
+            let inner =
+                FeatureResolverBackgroundLoop::new(posthog_client_config, shutdown_pageserver);
             let inner = Arc::new(inner);
 
             // The properties shared by all tenants on this pageserver.