fix: Create one consumer group per server+database

This hasn't caused any problems for me yet, but seemed like a good idea
because we want to be sure we don't get any of Kafka's consumer
rebalancing if we have multiple partitions.

server/src/init.rs

@@ -530,9 +530,11 @@ impl InitStatus {
                 let rules = handle
                     .rules()
                     .expect("in this state rules should be loaded");
-                let write_buffer = WriteBufferConfig::new(&rules).context(CreateWriteBuffer {
-                    config: rules.write_buffer_connection.clone(),
-                })?;
+                let write_buffer = WriteBufferConfig::new(handle.server_id(), &rules).context(
+                    CreateWriteBuffer {
+                        config: rules.write_buffer_connection.clone(),
+                    },
+                )?;
 
                 handle
                     .advance_replay(preserved_catalog, catalog, write_buffer)

server/src/lib.rs

@@ -552,12 +552,13 @@ where
         .map_err(|e| Box::new(e) as _)
         .context(CannotCreatePreservedCatalog)?;
 
-        let write_buffer = write_buffer::WriteBufferConfig::new(&rules).map_err(|e| {
-            Error::CreatingWriteBuffer {
-                config: rules.write_buffer_connection.clone(),
-                source: e,
-            }
-        })?;
+        let write_buffer =
+            write_buffer::WriteBufferConfig::new(server_id, &rules).map_err(|e| {
+                Error::CreatingWriteBuffer {
+                    config: rules.write_buffer_connection.clone(),
+                    source: e,
+                }
+            })?;
         db_reservation.advance_replay(preserved_catalog, catalog, write_buffer)?;
 
         // no actual replay required

server/src/write_buffer.rs

@@ -1,5 +1,8 @@
 use async_trait::async_trait;
-use data_types::database_rules::{DatabaseRules, WriteBufferConnection};
+use data_types::{
+    database_rules::{DatabaseRules, WriteBufferConnection},
+    server_id::ServerId,
+};
 use entry::{Entry, Sequence, SequencedEntry};
 use futures::{stream::BoxStream, StreamExt};
 use rdkafka::{
@@ -22,7 +25,10 @@ pub enum WriteBufferConfig {
 }
 
 impl WriteBufferConfig {
-    pub fn new(rules: &DatabaseRules) -> Result<Option<Self>, WriteBufferError> {
+    pub fn new(
+        server_id: ServerId,
+        rules: &DatabaseRules,
+    ) -> Result<Option<Self>, WriteBufferError> {
         let name = rules.db_name();
 
         // Right now, the Kafka producer and consumers ar the only production implementations of the
@@ -36,7 +42,7 @@ impl WriteBufferConfig {
                 Ok(Some(Self::Writing(Arc::new(kafka_buffer) as _)))
             }
             Some(WriteBufferConnection::Reading(conn)) => {
-                let kafka_buffer = KafkaBufferConsumer::new(conn, name)?;
+                let kafka_buffer = KafkaBufferConsumer::new(conn, server_id, name)?;
 
                 Ok(Some(Self::Reading(Arc::new(kafka_buffer) as _)))
             }
@@ -174,6 +180,7 @@ impl WriteBufferReading for KafkaBufferConsumer {
 impl KafkaBufferConsumer {
     pub fn new(
         conn: impl Into<String>,
+        server_id: ServerId,
         database_name: impl Into<String>,
     ) -> Result<Self, KafkaError> {
         let conn = conn.into();
@@ -183,7 +190,9 @@ impl KafkaBufferConsumer {
         cfg.set("bootstrap.servers", &conn);
         cfg.set("session.timeout.ms", "6000");
         cfg.set("enable.auto.commit", "false");
-        cfg.set("group.id", "placeholder");
+        // Create a unique group ID for this database's consumer as we don't want to create
+        // consumer groups.
+        cfg.set("group.id", &format!("{}-{}", server_id, database_name));
 
         let consumer: StreamConsumer = cfg.create()?;
         let mut topics = TopicPartitionList::new();