Parallelize MySQL server startup across nodes

Use ThreadPoolExecutor to start all 3 MySQL nodes concurrently.
Pre-compute shared cert chain. Failure on any node propagates via
future.result(). Reduces MySQL startup from ~5 min to ~2 min.

Closes #44

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: szachovy

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Dependabot updates for `github-actions` and `terraform` ecosystems. (#29)
 * CI workflow to build and push service images to GitHub Container Registry on master merge. (#97)
 * Pull-first with local build fallback for container images during deployment. (#97)
+* Parallelize MySQL server startup across all 3 nodes with ThreadPoolExecutor. (#44)
 
 ### Changed
 

src/initialize.py

@@ -56,6 +56,7 @@
 import sys
 import re
 import socket
+from concurrent.futures import ThreadPoolExecutor, as_completed
 
 import crypto
 import decorators
@@ -160,7 +161,12 @@ def get_mylogin_cnf(self, node: remote.RemoteConnection) -> bytes:
         raise ValueError("Fetched MYSQL_TEST_LOGIN_FILE invalid")
 
     def start_mysql_servers(self) -> None:
-        for node in self.mysql_nodes:
+        ca_key_pem = self.cert_manager.deserialization(self.ca_key)
+        ca_chain_pem = "".join(
+            self.cert_manager.deserialization(node.certificate) for node in self.mysql_nodes
+        ) + self.cert_manager.deserialization(self.ca_certificate)
+
+        def start_single_node(node: remote.RemoteConnection) -> None:
             node.upload_directory(
                 local_directory_path="./services/mysql-server",
                 remote_directory_path="/opt/superset-cluster/mysql-server"
@@ -170,11 +176,10 @@ def start_mysql_servers(self) -> None:
                 remote_file_path="/opt/superset-cluster/mysql-server/mysql_root_password"
             )
             node.upload_file(
-                content=self.cert_manager.deserialization(self.ca_key),
+                content=ca_key_pem,
                 remote_file_path="/opt/superset-cluster/mysql-server/superset_cluster_ca_key.pem")
             node.upload_file(
-                content="".join(self.cert_manager.deserialization(node.certificate) for node in self.mysql_nodes)
-                + self.cert_manager.deserialization(self.ca_certificate),
+                content=ca_chain_pem,
                 remote_file_path="/opt/superset-cluster/mysql-server/superset_cluster_ca_certificate.pem"
             )
             node.upload_file(
@@ -191,6 +196,11 @@ def start_mysql_servers(self) -> None:
                 ).run_mysql_server()"
             )
 
+        with ThreadPoolExecutor(max_workers=3) as executor:
+            futures = {executor.submit(start_single_node, node): node for node in self.mysql_nodes}
+            for future in as_completed(futures):
+                future.result()
+
     def start_mysql_mgmt(self, node: remote.RemoteConnection, state: str, priority: int) -> None:
         node.upload_directory(
             local_directory_path="./services/mysql-mgmt",