Health checks configuration in AWS - Step-by-Step Execution

Process Flow - Health checks configuration

Start: Configure Health Check

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Set Protocol, Port, Path

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Define Interval & Timeout

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Set Healthy & Unhealthy Thresholds

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Load Balancer Sends Health Requests

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Check Response: Success or Fail

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Update Instance Health Status

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Use Health Status for Traffic Routing

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End

This flow shows how health checks are configured and used to monitor instance health and route traffic accordingly.

Execution Sample

AWS

HealthCheck:
  Protocol: HTTP
  Port: 80
  Path: /health
  IntervalSeconds: 30
  TimeoutSeconds: 5
  HealthyThresholdCount: 3
  UnhealthyThresholdCount: 2

Defines a health check that sends HTTP requests every 30 seconds to /health on port 80, marking instances healthy or unhealthy based on response.

Process Table

Step	Action	Health Check Request Sent	Response Received	Health Status Update	Traffic Routing
1	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 1	Instance does not receive traffic
2	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 2	Instance does not receive traffic
3	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 3 (healthy threshold met)	Instance confirmed healthy, receives traffic
4	Send health check to instance	HTTP GET /health on port 80	500 Error	Instance marked unhealthy count 1	Instance still receives traffic
5	Send health check to instance	HTTP GET /health on port 80	Timeout	Instance marked unhealthy count 2 (unhealthy threshold met)	Instance marked unhealthy, traffic stopped
6	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 1	Instance still does not receive traffic
7	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 2	Instance still does not receive traffic
8	Send health check to instance	HTTP GET /health on port 80	200 OK	Instance marked healthy count 3 (healthy threshold met)	Instance marked healthy, traffic resumes
9	End monitoring	No request	No response	Health check monitoring continues	Traffic routed based on latest health status

💡 Health check monitoring runs continuously; traffic routing updates based on health status thresholds.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	Final
HealthyCount	0	1	2	3	0	0	1	2	3	3
UnhealthyCount	0	0	0	0	1	2	0	0	0	0
InstanceHealth	Unknown	Healthy (pending)	Healthy (pending)	Healthy	Unhealthy (pending)	Unhealthy	Unhealthy (pending)	Unhealthy (pending)	Healthy (pending)	Healthy
TrafficRouting	No traffic	No traffic	No traffic	Receives traffic	Receives traffic	No traffic	No traffic	No traffic	Receives traffic	Receives traffic

Key Moments - 3 Insights

Why does the instance not immediately become healthy after one successful health check?

Because the HealthyThresholdCount is 3, the instance must pass 3 consecutive successful checks before being marked healthy, as shown in steps 1-3 in the execution_table.

Why does traffic stop only after two failed health checks?

The UnhealthyThresholdCount is 2, so the instance must fail 2 consecutive checks before being marked unhealthy and traffic is stopped, as seen in steps 4-5.

What happens if the instance recovers after being unhealthy?

It must pass the healthy threshold count again (3 successful checks) before traffic resumes, as shown in steps 6-8.

Visual Quiz - 3 Questions

Look at the execution_table, what is the HealthyCount after step 3?

A 2

B 3

C 1

D 0

💡 Hint

Check the 'HealthyCount' variable in variable_tracker after step 3.

At which step does the instance stop receiving traffic due to health check failure?

A Step 4

B Step 3

C Step 5

D Step 6

💡 Hint

Look at the 'TrafficRouting' column in execution_table where traffic changes to stopped.

If the UnhealthyThresholdCount was set to 1, how would the traffic routing change after step 4?

A Traffic would stop immediately after step 4

B Traffic would continue as normal

C Traffic would stop after step 5

D Traffic would never stop

💡 Hint

Refer to how UnhealthyThresholdCount affects traffic routing in execution_table steps 4 and 5.

Concept Snapshot

Health checks monitor instance health by sending requests at intervals.
Set protocol, port, and path for checks.
Define thresholds for healthy/unhealthy counts.
Instance marked healthy after consecutive successes.
Instance marked unhealthy after consecutive failures.
Traffic routed only to healthy instances.

Full Transcript

Health checks configuration involves setting up periodic requests from a load balancer to instances to verify their health. The configuration includes protocol, port, path, interval, timeout, and thresholds for marking instances healthy or unhealthy. The load balancer sends requests at the defined interval and waits for responses within the timeout. If an instance responds successfully enough times consecutively, it is marked healthy and receives traffic. If it fails enough times consecutively, it is marked unhealthy and traffic is stopped. This process repeats continuously to ensure traffic is only sent to healthy instances.