本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# RDS Proxy 命令列範例
<a name="rds-proxy.examples"></a>

 若要查看連線命令和 SQL 陳述式的組合如何與 RDS Proxy 互動，請參閱下列範例。

**範例**
+  [Preserving Connections to a MySQL Database Across a Failover](#example-mysql-preserve-connections) 
+  [Adjusting the max_connections Setting for an Aurora DB Cluster](#example-adjust-cluster-max-connections) 

**Example 透過容錯移轉保留與 MySQL 資料庫的連線**  
 此 MySQL 範例將示範已開啟的連線如何在容錯移轉期間繼續運作。例如，當您重新啟動資料庫，或資料庫因由於有問題而無法使用時。本範例使用一個名為 `the-proxy` 的代理，以及一個具有資料庫執行個體 `instance-8898` 和 `instance-9814` 的 Aurora 資料庫叢集。從 Linux `failover-db-cluster` 命令列執行命令時，代理連線的寫入器執行個體會變更為不同的資料庫執行個體。您可以看到與代理關聯的資料庫執行個體改變了，但連線仍然保持開啟。  

```
$ mysql -h the-proxy.proxy-demo.us-east-1.rds.amazonaws.com -u admin_user -p
Enter password:
...

mysql> select @@aurora_server_id;
+--------------------+
| @@aurora_server_id |
+--------------------+
| instance-9814      |
+--------------------+
1 row in set (0.01 sec)

mysql>
[1]+  Stopped                 mysql -h the-proxy.proxy-demo.us-east-1.rds.amazonaws.com -u admin_user -p
$ # Initially, instance-9814 is the writer.
$ aws rds failover-db-cluster --db-cluster-identifier cluster-56-2019-11-14-1399
JSON output
$ # After a short time, the console shows that the failover operation is complete.
$ # Now instance-8898 is the writer.
$ fg
mysql -h the-proxy.proxy-demo.us.us-east-1.rds.amazonaws.com -u admin_user -p

mysql> select @@aurora_server_id;
+--------------------+
| @@aurora_server_id |
+--------------------+
| instance-8898      |
+--------------------+
1 row in set (0.01 sec)

mysql>
[1]+  Stopped                 mysql -h the-proxy.proxy-demo.us-east-1.rds.amazonaws.com -u admin_user -p
$ aws rds failover-db-cluster --db-cluster-identifier cluster-56-2019-11-14-1399
JSON output
$ # After a short time, the console shows that the failover operation is complete.
$ # Now instance-9814 is the writer again.
$ fg
mysql -h the-proxy.proxy-demo.us-east-1.rds.amazonaws.com -u admin_user -p

mysql> select @@aurora_server_id;
+--------------------+
| @@aurora_server_id |
+--------------------+
| instance-9814      |
+--------------------+
1 row in set (0.01 sec)
+---------------+---------------+
| Variable_name | Value         |
+---------------+---------------+
| hostname      | ip-10-1-3-178 |
+---------------+---------------+
1 row in set (0.02 sec)
```

**Example 調整 Aurora 資料庫叢集的 max\$1connections 設定**  
 此範例示範如何調整 Aurora MySQL 資料庫叢集的 `max_connections` 設定。若要這麼做，請根據 MySQL 5.7 相容叢集的預設參數設定，建立自己的資料庫叢集參數群組。您可以為 `max_connections` 設定指定一個值，以取代設定預設值的公式。將該資料庫叢集參數群組與資料庫叢集相關聯。  

```
export REGION=us-east-1
export CLUSTER_PARAM_GROUP=rds-proxy-mysql-57-max-connections-demo
export CLUSTER_NAME=rds-proxy-mysql-57

aws rds create-db-parameter-group --region $REGION \
  --db-parameter-group-family aurora-mysql5.7 \
  --db-parameter-group-name $CLUSTER_PARAM_GROUP \
  --description "Aurora MySQL 5.7 cluster parameter group for RDS Proxy demo."

aws rds modify-db-cluster --region $REGION \
  --db-cluster-identifier $CLUSTER_NAME \
  --db-cluster-parameter-group-name $CLUSTER_PARAM_GROUP

echo "New cluster param group is assigned to cluster:"
aws rds describe-db-clusters --region $REGION \
  --db-cluster-identifier $CLUSTER_NAME \
  --query '*[*].{DBClusterParameterGroup:DBClusterParameterGroup}'

echo "Current value for max_connections:"
aws rds describe-db-cluster-parameters --region $REGION \
  --db-cluster-parameter-group-name $CLUSTER_PARAM_GROUP \
  --query '*[*].{ParameterName:ParameterName,ParameterValue:ParameterValue}' \
  --output text | grep "^max_connections"

echo -n "Enter number for max_connections setting: "
read answer

aws rds modify-db-cluster-parameter-group --region $REGION --db-cluster-parameter-group-name $CLUSTER_PARAM_GROUP \
  --parameters "ParameterName=max_connections,ParameterValue=$$answer,ApplyMethod=immediate"

echo "Updated value for max_connections:"
aws rds describe-db-cluster-parameters --region $REGION \
  --db-cluster-parameter-group-name $CLUSTER_PARAM_GROUP \
  --query '*[*].{ParameterName:ParameterName,ParameterValue:ParameterValue}' \
  --output text | grep "^max_connections"
```