Questions and Answers
What is ClassicLink?
What does ClassicLink cost?
No additional charge, but existing cross Availability Zone data transfer charges apply.
How do I use ClassicLink?
Enable at least one VPC for ClassicLink and associate a Security Group from that VPC with the EC2-Classic instance.
Does the EC2-Classic instance become a member of the VPC?
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Can I use EC2 public DNS hostnames from my EC2-Classic and EC2-VPC instances to address each other?
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Are there any VPCs for which I cannot enable ClassicLink?
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Can traffic from an EC2-Classic instance travel through the Amazon VPC and use the Internet gateway?
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Does ClassicLink affect access control between EC2-Classic instances?
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Will ClassicLink settings on my EC2-Classic instance persist through stop/start cycles?
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Will my EC2-Classic instance be assigned a new private IP address after enabling ClassicLink?
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Does ClassicLink allow EC2-Classic Security Group rules to reference VPC Security Groups?
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Study Notes
ClassicLink Overview
- ClassicLink connects EC2 instances on the EC2-Classic platform with instances in a VPC using private IP addresses.
- Requires enabling ClassicLink for a VPC and associating a Security Group from the VPC with an EC2-Classic instance.
Pricing Information
- No extra charge for ClassicLink use, but data transfer charges between Availability Zones apply.
Usage Steps
- Enable at least one VPC for ClassicLink in your account.
- Associate a Security Group from the VPC to the desired EC2-Classic instance.
- An EC2-Classic instance can only be linked to one VPC at a time.
Membership and Security Groups
- An EC2-Classic instance does not become a part of the VPC; it joins the VPC Security Group associated with it.
- All VPC Security Group rules govern communication with the EC2-Classic instance.
DNS and IP Communication
- EC2 public DNS hostnames do not resolve to private IP addresses across EC2-Classic and EC2-VPC instances.
VPC Eligibility
- ClassicLink cannot be enabled for VPCs with a CIDR in the 10.0.0.0/8 range, except for 10.0.0.0/16 and 10.1.0.0/16.
- VPCs with route table entries directing to the 10.0.0.0/8 CIDR to non-local targets cannot enable ClassicLink.
Traffic Routing
- Traffic from EC2-Classic instances can only route to private IPs within the VPC.
- Cannot route traffic to external destinations such as internet gateways or peered VPCs.
Access Control
- ClassicLink does not alter the existing Security Group access control for EC2-Classic instances.
Instance Cycles
- ClassicLink connections do not persist through stop/start cycles; they need to be re-established.
- Connection does persist through instance reboots.
IP Addressing
- Enabling ClassicLink does not assign a new private IP address; the existing private IP remains for communication with VPC resources.
Security Group References
- EC2-Classic Security Group rules cannot reference VPC Security Groups and vice versa.
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Description
This quiz covers the essential aspects of ClassicLink, including how it connects EC2 instances on the EC2-Classic platform with those in a VPC. Learn about pricing, usage steps, security group associations, and important DNS considerations. Perfect for understanding VPC connectivity and management.
