AWS Lambda function Python script Task timed out error

Question

I was tried to connect into RDS postgresql database using Lambda function. Lambda function returning timed out error. Here is the source code.

postgres_test.py:

import sys
import logging
import psycopg2

from db_util import make_conn, fetch_data
def lambda_handler(event, context):
    query_cmd = "SELECT COUNT(*) FROM users"
    # print query_cmd

    # get a connection, if a connect cannot be made an exception will be raised here
    conn = make_conn()

    result = fetch_data(conn, query_cmd)
    conn.close()

    return result

db_util.py:

import psycopg2

db_host = "db_host"
db_port = 5432
db_name = "db_name"
db_user = "db_user"
db_pass = "db_pass"
db_table = "db_table"


def make_conn():
    conn = None
    try:
        conn = psycopg2.connect("dbname='%s' user='%s' host='%s' password='%s'" % (db_name, db_user, db_host, db_pass))
    except:
        print ("I am unable to connect to the database")
    return conn


def fetch_data(conn, query):
    result = []
    print ("Now executing: " + query)
    cursor = conn.cursor()
    cursor.execute(query)

    raw = cursor.fetchall()
    for line in raw:
        result.append(line)

    return result

here is the execution results:

Test Event Name
triggers3event

Response
{
  "errorMessage": "2021-10-19T22:55:12.543Z 207db48f-eb82-4bbd-afd5-1836b63874cf Task timed out after 3.00 seconds"
}

Function Logs
START RequestId: 207db48f-eb82-4bbd-afd5-1836b63874cf Version: $LATEST
END RequestId: 207db48f-eb82-4bbd-afd5-1836b63874cf
REPORT RequestId: 207db48f-eb82-4bbd-afd5-1836b63874cf  Duration: 3003.71 ms    Billed     Duration: 3000 ms    Memory Size: 128 MB Max Memory Used: 12 MB  
2021-10-19T22:55:12.543Z 207db48f-eb82-4bbd-afd5-1836b63874cf Task timed out after 3.00 seconds

Request ID
207db48f-eb82-4bbd-afd5-1836b63874cf

Pls help me to fix following issue. I am not sure what was wrong from above codes.

Answer 1

It might simply take your code more than 3 seconds to connect and retrieve data, so your Lambda function times out. You have the default setting of 3 seconds, as you can see in the CloudWatch Logs):

Task timed out after 3.00 seconds

Increase the timeout and the configured RAM size for the Lambda (which will give the Lambda function proportionally more CPU and make it run faster) and retry.

If that also fails, then the problem may be that your Lambda function has no network route to the RDS database. Having no route can cause the DB connection attempt to hang and the Lambda function to time out.

From the information you've provided in comments below, it looks like the RDS database is actually running in a different AWS account but is accessible publicly. This suggests that your Lambda function may be configured incorrectly. If you don't need the Lambda function to run in a VPC then don't configure it to run in VPC - see the Lambda function VPC configuration options and remove the subnet assignment(s).

Answer 2

Usually the reason Lambda function times out is due to configuration of Security Groups.

In order to rectify, please follow these suggestions:

1. Check whether the Lambda and corresponding db service is in same VPC

2. Check whether the Security Group is allowing the connection

3. If you are connecting the db over internet, check the connection. (If you are in VPC, see you are routing via NAT and IG)

Again, reiterating one more time, that many times, timed out issue is to due to network allow/deny, so in case of Lambda, a Security Group issue.