EC2 instance has no public DNS

Question

A guy I work with gave me the EC2 credentials to log onto his EC2 console  I was not the one who set it up  Some of the instances show a public dns name and others have a blank public DNS  I want to be able to connect to the instances that have a blank public DNS  I have not been able to figure out why these show up as blank

User · Answer

For me problem was in subnet settings    Open https   console aws amazon com vpc Go to subnets in left menu Choose your subnet Modify auto-assigning IP settings to enable

User · Answer

Go to  AWS Console  Go to  Services and select VPC Click on vpc  select the instance and click on Action  Select  Edit DNS Host name click on yes    At the end you will get your Public dns

User · Answer

If the instance is in VPC  make sure both  DNS resolution  and  DNS hostnames  is set to  yes   You can do this in the Aws console UI  HTH

User · Answer

Go to VPC console  select your VPC  and click ACTIONS menu  select Edit DNS Hostnames - select Yes  That should fix it

User · Answer

After verifying VPC and Subnet settings  my EC2 instance still didn t have a public DNS  After a day of searching for a resolution  I finally figured it out   I had to create a new Elastic IP address  then associate it to my instance   From the EC2 Dashboard   Go to Elastic IPs from the sidebar    Click Allocate new address  then Allocate   Go back to the EC2 Dashboard  Go to Network Interfaces   Select the EC2 instance without a public DNS  Then Actions - Associate Address   The Address field  select the new elastic IP address   The Associate to private IP address field  select the private IP address with no public DNS   Click Associate Address   Your EC2 instance should now have a public DNS

User · Answer

This is the tip provided to resolve the issue which does not work   Tip - If your instance doesn t have a public DNS name  open the VPC console  select the VPC  and check the Summary tab  If either DNS resolution or DNS hostnames is no  click Edit and change the value to yes   Assuming you have done this and you are still not getting a Public IP then go over to the subnet in question in the VPC admin screen and you will probably discover  Auto-Assign Public IP  is not set to yes   Modify that setting then  and I know you don t want to here this  create a new instance in that subnet   As far as I can tell you cannot modify this on the host  I tried and tried  just terminate it

User · Answer

Here I will summarize the most common issues that occur   When you create a custom VPC  if you want aws resources such as ec2 instances to acquire public IP addresses so that the internet can communicate with them  then you first must ensure that the ec2 instance is associated with a public subnet of the custom VPC  This means that subnet has an internet gateway associated with it  Also  you need to ensure that the security group of the VPC associated with ec2 instance has rules allowing inbound traffic to the desired ports  such as ssh  http and https  BUT here are some common oversights that still occur   1  You must ensure that DNS hostnames is enabled for the VPC  2  You must ensure the public subnet linked to the EC2 instance has its  auto-assignment of public ip  flag enabled  3  If the instance is already created  then you might need to terminate it and create a new instance for the public IP and public DNS fields to be populated

User · Answer

First of all  there can be two reasons for this    You have created your own VPC and forgot to enable Public DNS    To solve this     i  Go to AWS VPC console and select the VPC you have created    ii  Then click on Actions and then enable DNS Resolution               OR    You have not enabled public ip-assign option in EC2 configuration    Here you cannot change the setting  so create an ami image and then recreate the instance from that

User · Answer

The change to the DNS Hostnames setting can also be done using the AWS CLI   aws ec2 modify-vpc-attribute --vpc-id  vpc id --enable-dns-hostnames    Value   true      Where  vpc id is the ID of the VPC that your instance is attached to    As soon as the VPC is updated the instance will gain a public DNS

User · Answer

There is a actually a setting in the VPC called  DNS Hostnames   You can modify the VPC in which the EC2 instance exists  and change this to  Yes   That should do the trick   I ran into this issue yesterday and tried the above answer from Manny  which did not work  The VPC setting  however  did work for me   Ultimately I added an EIP and I use that to connect

User · Answer

I had the same problem an solved it  Have a look at the step-by-step instructions    Go to console aws amazon com Go To Services -  VPC Open Your VPCs select your VPC connected to your EC2 and select Actions    Edit DNS Hostnames ---  Change DNS hostnames  to YES   Hope this helps   Cheers

User · Answer

For those using CloudFormation  the key properties are EnableDnsSupport and EnableDnsHostnames which should be set to true  VPC        Type   AWS  EC2  VPC       Properties          CidrBlock   10 0 0 0 16         EnableDnsSupport  true        EnableDnsHostnames  true        InstanceTenancy   default         Tags                        Key   env             Value   dev

User · Answer

In my case I found the answer from slayedbylucifer and others that point to the same are valid  Even it is set that DNS hostname  yes  no Public IP is assigned on my-pvc  only Privat IP         It is definitely that Auto assign Public IP has to be set Enable    If it is not selected  then by default it sets to Use subnet setting  Disable

User · Answer

You don t have to assign public ip address to your instance  you can use NAT instances or NAT Gateway   https   docs aws amazon com vpc latest userguide VPC Scenario2 html https   docs aws amazon com vpc latest userguide vpc-nat-comparison html

User · Answer

Go to VPC Select your VPC Click actions and choose Edit DNS hostnames Tick Enable for DNS Hostnames Click save changes

User · Answer

Sounds like the instance was launched in VPC and while doing so  the check-box for Automatically assign a public IP address to your instances was not checked  Hence the instance does not have a public IP  You can assign an Elastic IP to this instance and then log in using that IP

User · Answer

It is related to the VPC s feature called  DNS Hostnames   You can enable or disable it   Go to the VPC  under the Actions menu select the  Edit DNS Hostnames  item and then choose  Yes   After doing so  the public DNS of the EC2 instances should be displayed

User · Answer

I tried to fix the  no public DNS   once the EC2 was up and running  I couldnt add a public DNS  this is even after following the above steps making mods to the VPC or the Subnet  so  I had to make modifications to the subnet and the vpc  before starting another instance  and THEN start up a new instance   the new instance had a public DNS    That is how it worked for me

User · Answer

Just launch another instance  and also delete the one in question if it has no use  and make sure this time you check  Autoatically assign a public IP address to your instance     If not then as slayedbylucifer suggested  assign an Elastic IP  EIP  to the instance and then log in using that IP   Be careful though  if you are running the free AWS tier  an EIP will cost you money-- that s a whole  nother topic

[amazon-web-services] EC2 instance has no public DNS

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