# RDS Proxy 命令行示例
<a name="rds-proxy.examples"></a>

 要了解连接命令和 SQL 语句的组合如何与 RDS Proxy 交互，请查看以下示例。

**示例**
+  [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 在故障转移时保留与 MySQL 数据库的连接**  
 此 MySQL 示例演示在失效转移期间打开的连接如何继续工作。例如，当您重启数据库或数据库由于某个问题而变得不可用时。本示例使用一个名为 `the-proxy` 的代理，以及一个包含数据库实例 `instance-8898` 和 `instance-9814` 的 Aurora 数据库集群。从 Linux 命令行运行 `failover-db-cluster` 命令时，代理连接到的写入器实例将更改为不同的数据库实例。您可以看到，与代理关联的数据库实例在连接保持打开状态时发生更改。  

```
$ 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 调整 Aurora 数据库集群的 max\$1connections 设置**  
 本示例演示如何调整 Aurora MySQL 数据库集群的 `max_connections` 设置。为此，请根据与 MySQL 5.7 兼容的集群的原定设置参数设置，创建自己的数据库集群参数组。您可以为 `max_connections` 设置指定一个值，从而覆盖设置默认值的公式。将数据库集群参数组与数据库集群关联。  

```
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"
```