AWS ELB

As the name Elastic Load Balancer says it balances the load by routing traffic across multiple targets. Good place to configure and debug how the flow of traffic goes with in AWS.

Notes

Useful AWS commands

aws elbv2 describe-load-balancers --query 'LoadBalancers[].LoadBalancerName'
aws elbv2 describe-load-balancers --query 'LoadBalancers[].[LoadBalancerName,LoadBalancerArn]'


lb_arn=$(aws elbv2 describe-load-balancers --names "$1" --query 'LoadBalancers[].[LoadBalancerArn]' --output text)

listener_arn=$(aws elbv2 describe-listeners --load-balancer-arn "$lb_arn" --query 'Listeners[].{ListenerArn:ListenerArn,Protocol:Protocol,Port:Port}' | jq -r ".[] | select(.Port=="$2").ListenerArn")

aws elbv2 describe-rules --listener-arn "$listnerarn" --query 'Rules[].{Priority:Priority,Host:Conditions[0].Values[0]}' | jq

Useful scripts

Python script which prints all the hostnames used in the load balancer rounting rule. Change the log level to DEBUG to back trace.

import boto3
from pprint import pprint
import json
import logging
import sys


logger = logging.getLogger('print-aws')
logger.setLevel(logging.INFO)
sh = logging.StreamHandler(sys.stdout)
formatter = logging.Formatter('[%(asctime)s] %(levelname)s [%(filename)s.%(funcName)s:%(lineno)d] %(message)s', datefmt='%a, %d %b %Y %H:%M:%S')
sh.setFormatter(formatter)
logger.addHandler(sh)

elbv2 = boto3.client("elbv2")


def printEndPointUrls():
    response= elbv2.describe_load_balancers()
    loadbalancers = response["LoadBalancers"][2:]
    logger.debug(response)
    for lb in loadbalancers:
        lbArn=lb["LoadBalancerArn"]
        printLBListeners(lbArn)


def printLBListeners(lbArn):
    logger.debug(lbArn)
    response = elbv2.describe_listeners(LoadBalancerArn=lbArn)
    listeners = response["Listeners"]
    logger.debug(listeners)
    for listener in listeners:
        if listener["Protocol"] == "HTTPS" and listener["Port"] == 443:
            if not listener["DefaultActions"]:
                logger.debug(listener["DefaultActions"][0]["RedirectConfig"]["Host"])
            listenerArn = listener["ListenerArn"]
            printListenerRules(listenerArn)


def printListenerRules(listenerArn):
    logger.debug("printing Listener Rules...")
    try:
        response = elbv2.describe_rules(ListenerArn=listenerArn)
        logger.debug(response)
        if response["Rules"]:
            for rule in response["Rules"]:
                logger.debug(rule)
                printRule(rule)
    except Exception as e:
        logger.error(e)
        return



def printRule(rule):
    try:
        if rule["Conditions"]:
            for condition in rule["Conditions"]:
                if condition["Field"] == "host-header":
                    print(*condition["Values"], sep = "\n")
    except Exception as e:
        logger.error("Error at printing rule \n %s", json.dumps(rule, indent=2))
        logger.error(e)
        return


if __name__ == "__main__":
    print(printEndPointUrls())
        #print(printListenerRules("arn:aws:elasticloadbalancing:......"))

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