Lab3.1: failing in trying to pull docker.io/library/python:3--no such host

caishaoping

Here there,
is there any registry needed on my VM before pulling image to docker.io? I am failing building docker image for lab3.1.

1. Below is the command:
   vagrant@cp:~/app1$ sudo podman build -t simpleapp .

2. Error message from the command:
   STEP 1/4: FROM python:3
   ✔ docker.io/library/python:3
   Trying to pull docker.io/library/python:3...
   Error: error creating build container: initializing source docker://python:3: pinging container registry registry-1.docker.io: Get "https://registry-1.docker.io/v2/": dial tcp: lookup registry-1.docker.io: no such host

3. nslookup to verify that registry-1.docker.io is accessible:
   vagrant@cp:~/app1$ nslookup registry-1.docker.io
   Server: 127.0.0.53
   Address: 127.0.0.53#53

Non-authoritative answer:
Name: registry-1.docker.io
Address: 54.83.42.45
Name: registry-1.docker.io
Address: 54.242.59.189
Name: registry-1.docker.io
Address: 3.215.51.67
** server can't find registry-1.docker.io: NXDOMAIN

vagrant@cp:~/app1$

where else should I check? Thanks

Shao

chrispokorni

Hi @caishaoping,

During the exam you will be provided with a pre-built environment with the necessary virtual instances for nodes. For additional exam related details you can examine the candidate handbook for CKAD, or additional certification exam-specific questions may be answered by the LF support team by opening a ticket at trainingsupport.linuxfoundation.org.

Regards,
-Chris

chrispokorni

Hi @caishaoping,

It seems that your custom Ubuntu distribution behaves differently than the official and the cloud distros. Name resolution is not working as expected, so I would recommend editing /etc/resolv.conf on both nodes to add a popular nameserver to fix the DNS issues.

Regards,
-Chris

caishaoping

Just wanted to follow up with update of my way of resolution to fix the issue, "netplan" was new to me. Here is what I did:

1. before change:

vagrant@cp:~/app1$ cat /etc/netplan/50-vagrant.yaml

network:
version: 2
renderer: networkd
ethernets:
eth1:
addresses:
- 172.16.0.100/24

2. Vim to chagne:
   vagrant@cp:~/app1$ sudo vim /etc/netplan/50-vagrant.yaml

3. After the change:

vagrant@cp:~/app1$ sudo cat /etc/netplan/50-vagrant.yaml

network:
version: 2
renderer: networkd
ethernets:
eth1:
addresses:
- 172.16.0.100/24
nameservers:
addresses: [1.1.1.1,1.0.0.1,8.8.8.8,8.8.4.4]

4. vagrant@cp:~/app1$ sudo netplan try
   Do you want to keep these settings?
   Press ENTER before the timeout to accept the new configuration
   Changes will revert in 115 seconds

5. vagrant@cp:~/app1$ sudo netplan apply

6. vagrant@cp:~/app1$ sudo podman build -t simpleapp .

STEP 1/4: FROM python:3
✔ docker.io/library/python:3
Trying to pull docker.io/library/python:3...
Getting image source signatures
Copying blob d8092d56ded5 done
Copying blob 3e94d13e55e7 done
Copying blob 1671565cc8df done
Copying blob 53ad072f9cd1 done
Copying blob fa9c7528c685 done
Copying blob d6b983117533 done
Copying blob 102b77c1d556 done
Copying blob c65fe89c654d done
Copying blob 18db97afaa16 done
Copying config 4f9baf941f done
Writing manifest to image destination
Storing signatures
STEP 2/4: ADD simple.py /
.
.
.

caishaoping

Hi @chrispokorni,

Yes, my VM is using Chef's 'bento/ubuntu-20.04' version '202206.03.0', will this flavor of Ubuntu give me any difference in CKAD certification testing?

As to /etc/resolv.conf, I did not have to add new nameservers, instead, I used netplan to apply changes of nameservers, will look further which resolv file is updated by netplan tool.

Thanks
Shao