AWS Lambda RDS MySQL 数据库连接接口错误

Question

当我尝试连接到 AWS RDS (MySQL) 时，大部分时间我都会收到 InterfaceError。当我编辑 Lambda 代码并重新运行时，它第一次可以正常工作，但随后出现同样的错误。

我的代码：

import sys
import logging
import pymysql
import json
import traceback
rds_host  = "*****.rds.amazonaws.com"
name = "*****"
password = "****"
db_name = "myDB"
logger = logging.getLogger()
logger.setLevel(logging.INFO)
try:
    conn = pymysql.connect(rds_host, user=name, passwd=password, db=db_name, connect_timeout=5)
except:
    logger.error("ERROR: Unexpected error: Could not connect to MySql instance.")
    sys.exit()
logger.info("SUCCESS: Connection to RDS mysql instance succeeded")
def handler(event, context):
    sub = event['sub']
    username = event['username']
    givenname = event['givenname']
    isAdmin = event['isAdmin']
    print (sub)
    print (username)
    print (givenname)
    print (isAdmin)
    data = {}

    cur = conn.cursor()
    try:
        cmd = "SELECT AuthState FROM UserInfo WHERE UserName=" + "\'" + username + "\'"
        rowCnt = cur.execute(cmd)
        print (cmd)
    except:
        print("ERROR: DB Query Execution failed.")
        traceback.print_exc()
        data['errorMessage'] = 'Internal server error'
        response = {}
        response['statusCode'] = 500
        response['body'] =  data
        return response
    if rowCnt <= 0:
        print (username)
        data['errorMessage'] = 'No User Name Found'
        response = {}
        response['statusCode'] = 400
        response['body'] =  data
        conn.close()
        return response
    for row in cur:
        print row[0]
        if int(row[0]) == 0:#NOT_AUTHORIZED
            ret = "NOT_AUTHORIZED"
        elif int(row[0]) == 1:#PENDING
             ret = "PENDING"
        elif int(row[0]) == 2:#AUTHORIZED
            ret = "AUTHORIZED"
        else:#BLOCKED
            ret = "BLOCKED"
    data['state'] = ret
    response = {}
    response['statusCode'] = 200
    response['body'] =  data
    conn.close()
    return response

堆栈跟踪：

Traceback (most recent call last):
  File "/var/task/app.py", line 37, in handler
  File "/var/task/pymysql/connections.py", line 851, in query
    self._execute_command(COMMAND.COM_QUERY, sql)
  File "/var/task/pymysql/connections.py", line 1067, in _execute_command
    raise err.InterfaceError("(0, '')")
InterfaceError: (0, '')

Answer 1

阅读Understanding Container Reuse in Lambda。

它是关于 Node 的，但对于 Python 来说同样准确。

您的代码不会在每次调用时从顶部运行。有时它以handler 开头。

为什么？它更快。

你怎么知道什么时候会发生？您不会...除了每次重新部署该函数，当然，您总是会在第一次调用时获得一个新容器，因为旧容器会被重新部署所抛弃。

如果您要在处理程序之外进行数据库连接，请不要调用conn.close()，因为在下一次调用该函数时，您可能会发现您的容器仍然存在，并且使用已经关闭的数据库句柄调用处理程序。

您必须编写 Lambda 函数，这样它们既不会在容器被重用时失败，也不会在容器不被重用时失败。

更简单的解决方案是在处理程序中打开数据库连接。更复杂但更优化的解决方案（就运行时间而言）是永远不要关闭它，这样它就有可能被重用。