Fail proxy startup if brokerServiceURL is missing scheme (#14682)

Make Pulsar Proxy fail on start up with a helpful error message if the `brokerServiceURL` or the `brokerServiceURLTLS` configurations are invalid.

I recently ran into an issue where the configured URL did not have the `pulsar://` or the `pulsar+ssl://` prefix. It would have been very helpful if the proxy had just failed on startup when it had an invalid config.

* Update documentation
* Add validation checks to the `ProxyServiceStarter` class.

(cherry picked from commit 342a5df)
(cherry picked from commit 0a169d9)

conf/proxy.conf

@@ -25,7 +25,8 @@ zookeeperServers=
 # Configuration store connection string (as a comma-separated list)
 configurationStoreServers=
 
-# if Service Discovery is Disabled this url should point to the discovery service provider.
+# If Service Discovery is Disabled this url should point to the discovery service provider.
+# The URL must begin with pulsar:// for plaintext or with pulsar+ssl:// for TLS.
 brokerServiceURL=
 brokerServiceURLTLS=
 

pulsar-proxy/src/main/java/org/apache/pulsar/proxy/server/ProxyConfiguration.java

@@ -105,12 +105,12 @@ public class ProxyConfiguration implements PulsarConfiguration {
 
     @FieldContext(
         category = CATEGORY_BROKER_DISCOVERY,
-        doc = "The service url points to the broker cluster"
+        doc = "The service url points to the broker cluster. URL must have the pulsar:// prefix."
     )
     private String brokerServiceURL;
     @FieldContext(
         category = CATEGORY_BROKER_DISCOVERY,
-        doc = "The tls service url points to the broker cluster"
+        doc = "The tls service url points to the broker cluster. URL must have the pulsar+ssl:// prefix."
     )
     private String brokerServiceURLTLS;
 

pulsar-proxy/src/main/java/org/apache/pulsar/proxy/server/ProxyServiceStarter.java

@@ -136,6 +136,16 @@ public ProxyServiceStarter(String[] args) throws Exception {
                 config.setConfigurationStoreServers(configurationStoreServers);
             }
 
+            if (isNotBlank(config.getBrokerServiceURL())) {
+                checkArgument(config.getBrokerServiceURL().startsWith("pulsar://"),
+                        "brokerServiceURL must start with pulsar://");
+            }
+
+            if (isNotBlank(config.getBrokerServiceURLTLS())) {
+                checkArgument(config.getBrokerServiceURLTLS().startsWith("pulsar+ssl://"),
+                        "brokerServiceURLTLS must start with pulsar+ssl://");
+            }
+
             if ((isBlank(config.getBrokerServiceURL()) && isBlank(config.getBrokerServiceURLTLS()))
                     || config.isAuthorizationEnabled()) {
                 checkArgument(!isEmpty(config.getZookeeperServers()), "zookeeperServers must be provided");

site2/docs/reference-configuration.md

@@ -693,8 +693,8 @@ The [Pulsar proxy](concepts-architecture-overview.md#pulsar-proxy) can be config
 |forwardAuthorizationCredentials| Forward client authorization credentials to Broker for re-authorization, and make sure authentication is enabled for this to take effect. |false|
 |zookeeperServers|  The ZooKeeper quorum connection string (as a comma-separated list)  ||
 |configurationStoreServers| Configuration store connection string (as a comma-separated list) ||
-| brokerServiceURL | The service URL pointing to the broker cluster. | |
-| brokerServiceURLTLS | The TLS service URL pointing to the broker cluster | |
+| brokerServiceURL | The service URL pointing to the broker cluster. Must begin with `pulsar://`. | |
+| brokerServiceURLTLS | The TLS service URL pointing to the broker cluster. Must begin with `pulsar+ssl://`. | |
 | brokerWebServiceURL | The Web service URL pointing to the broker cluster | |
 | brokerWebServiceURLTLS | The TLS Web service URL pointing to the broker cluster | |
 | functionWorkerWebServiceURL | The Web service URL pointing to the function worker cluster. It is only configured when you setup function workers in a separate cluster. | |