• Create an internet gateway and attach it to the VPC.
• Add a route to the subnet’s route table that directs internet-bound traffic to the internet gateway.
• Make sure instances in the subnet have a globally unique IP address.
• Ensure that the network access control lists and security group rules allow the relevant traffic.

2. Instance in a private subnet with a NAT Gateway.

To connect to services outside the VPC we use a NAT gateway for instances in a private subnet. However, external services cannot initiate a connection with those instances.

To do so, we follow the steps below.

1. Initially, we open the Amazon VPC console.
2. In the navigation pane, we select NAT Gateways.
3. Then we select Create NAT Gateway and perform the below tasks:
   1. We specify a name for the NAT gateway if necessary.
   2. Select the subnet in which to create the NAT gateway.
   3. To create a private NAT gateway, we select Private or Public to create a public NAT gateway for Connectivity type.
   4. In the case of Public, for Elastic IP allocation ID, select an Elastic IP address.
   5. Finally, we select Create a NAT Gateway.
4. Once the status of the NAT gateway change from Pending to Available, it is ready to use.

3. Instance in a private subnet with a NAT Instance

To set up the VPC and NAT instance using the console, our Support Techs recommend these steps:

1. Initially, we create a VPC with two subnets.

1. 1. After creating, we attach an Internet gateway to the VPC
   2. Then we create a custom route table to send traffic destined outside the VPC to the internet gateway, and then associate it with one subnet, making it a public subnet.

2. Next, we create the NATSG security group.

3. To run as a NAT instance, we launch an instance into the public subnet from an AMI.

1. 1. Open the Amazon EC2 console.
   2. On the dashboard, we select the Launch Instance button, and complete the wizard as follows:
      1. On the Choose an Amazon Machine Image (AMI) page, we set the filter to Owned by me, then select the AMI.
      2. Then on the Choose an Instance Type page > select instance type > Configure Instance Details.
      3. On the Configure Instance Details page, select the VPC and select the public subnet.
      4. We can also add storage to the instance, and add tags. Once done, we select Next: Configure Security Group.
      5. Here, we select the Select an existing security group option, and select the NATSG security group > Review and Launch.
      6. Once done, review and make changes, and then select Launch.

4. Then we go ahead and disable the SrcDestCheck attribute for the NAT instance

5. Suppose we didn’t assign a public IP address to the NAT instance during launch. In that case, we associate an Elastic IP address with it.

1. 1. To do so, we open the Amazon VPC console.
   2. In the navigation pane > Elastic IPs > Allocate new address.
   3. After that, select the Elastic IP address from the list > Actions > Associate address.
   4. We select the network interface resource, then select the network interface for the NAT instance. Select the address to associate the Elastic IP with from the Private IP list > Associate.
   5. Then we update the main route table to send traffic to the NAT instance.

4. Instance in a private subnet with a proxy

We modify the /etc/yum.conf file to configure yum to use a proxy:

proxy=http://proxy-server-IP-address:proxy_port
proxy_username=proxy-user-name
proxy_password=proxy-password

4. Once we configure the instance using one of the preceding options, to confirm that the instance can access the repository we run:

Amazon Linux 1:

telnet repo.us-east-1.amazonaws.com 80

Amazon Linux 2:

telnet amazonlinux.us-east-1.amazonaws.com 80

Here, ensure to replace us-east-1 with the instance’s region.

[Need help with the fix? We’d be happy to assist you]

Conclusion

In short, we saw how our Support Techs fix the EC2 yum error for our customers.