Are EC2 security group changes effective immediately for running instances?

Question

I have an EC2 instance running, and it belongs to a security group. If I add a new allowed connection to that security group through AWS Management Console, should that change be effective immediately? Or perhaps only after restart of the instance?

In my case, I'm trying to allow access to PostgreSQL's default port (tcp 5432 5432 0.0.0.0/0), and I'm not sure if it's the EC2 firewall or PostgreSQL's settings that are refusing the connection.

Solution 1

Seems like yes (quoting AWS documentation):

You can modify rules for a group at any time. The new rules are automatically enforced for all running instances and instances launched in the future.

A simple test of disallowing access to a certain (previously accessible) port also confirmed this.

Solution 2

The 'listen_addresses' directive on postgresql.conf defaults to 127.0.0.1 only. It should be changed to listen_addresses = '*' to accept connections from 0.0.0.0/0

Comments

[Adrian Ionut]

I tested this and it's true.

[shonky linux user]

However when allowing access to a previously disallowed resource it can take up to a minute or two before the new policy becomes effective and access is granted.

[Admin]

I've had several instances where both allowing and disallowing have taken over 30 seconds to propagate. So instant is definitely not true. Pretty fast though... but be patient for a minute or two before drawing conclusions :)

[Ravinder Reddy]

Link posted in the answer seems broken as on today. Can someone correct it please?