Unable to update inside the Container

venugosr · 03-17-2020, 12:10 AM

Hi Team,

Please be informed that, I have installed CentOS 8 in my VMWare workstation.

After that I have installed the docker-ce without any issues.

Later i have pulled the httpd image.

Code:

docker container run --publish 8080:80 --detach httpd

Now entering inside the container and trying to update the same.

Code:

docker container exec -it 7d7 bash

Code:

root@7d73e397628d:/usr/local/apache2# apt update

When i execute the above command and getting the attached error. Please help me how to resolve this.

Note:
I have tried the same in Ubuntu which I have installed in same VMWare, but i did not face any issues.

Please help me to solve the issue.

berndbausch · 03-17-2020, 02:41 AM

Name resolution is not set up correctly in the container.

Check /etc/resolv.conf and fix it so that it points to a nameserver to which you have connectivity. For details, read Red Hat documentation.

EDIT: Oops, I misunderstood you. The container can't be running Centos, so disregard the documentation link. You need to follow instructions for the distro that runs in the container. Or perhaps the container is not supposed to be updated. Perhaps you should also read documentation pertaining to this particular container.

venugosr · 03-17-2020, 02:59 AM

Hi,

Could you please advise why the container can't be running in CentOS?
I have installed docker and pulled the httpd image in CentOS
Moreover I have tried the same in GCP cloud and it is working as expected.

My doubt is, do we need to change anything in the VMWare end or in the OS end?

berndbausch · 03-17-2020, 04:02 AM

I did not say that the container can't run in Centos.
I said that it can't be running Centos, since Centos doesn't use apt, and doesn't name the web server "apache2".
I also said that the name resolution in this container doesn't work. This is where you should start your troubleshooting.

venugosr · 03-17-2020, 05:58 PM

Hi,

You have taken the question other way around.

The base OS is CentOS 8 and i have installed in VMWare.

I have pulled the docker container image httpd.

The docker container image OS is Debian.

So i have used apt.

I ran the above commands in GCP it works as expected but not in VMWare.

To fix the issue i need help.

berndbausch · 03-17-2020, 11:32 PM

The name resolution doesn't work. Which DNS server is configured in the container?

It may work in GCP because the container gets the correct nameserver from DHCP. The problem in your VMware environment may be due to an incorrect or no DNS server sent by DHCP.

The nameserver is defined in /etc/resolv.conf or recently /etc/systemd/systemd-resoled.conf (from memory).

venugosr · 03-19-2020, 02:59 AM

Hi,

Sorry for the late reply.

I am not able to find the /etc/systemd/systemd-resoled.conf

Please find the below details from /etc/resolv.conf file

Code:

root@2e46bc93dfaf:/etc/systemd# cat /etc/resolv.conf
# Generated by NetworkManager
search server.com
nameserver 192.168.221.2
root@2e46bc93dfaf:/etc/systemd#

Please find the OS details of the container.

Code:

root@2e46bc93dfaf:/etc/systemd# cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 10 (buster)"
NAME="Debian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
root@2e46bc93dfaf:/etc/systemd#

Please note, I have installed Ubuntu variant and tried to do the same, it is working as expected.
The OS details of the container and resolv.conf file are same.

The only different is the base OS is Ubuntu instead of CentOS in VMWare.

I'm facing the same issue in real time as we are using the Linux OS in VMWare.

berndbausch · 03-19-2020, 06:04 AM

From what you say, it seems that 192.168.221.2 is correct. Perhaps the container has no connectivity to this address?

It's your job to find out why name resolution fails. The DNS server doesn't resolve deb.debian.org, or it doesn't exist, or it is not accessible, or perhaps there are other reasons.

Perhaps name resolution works now and it did not work for a limited time.

venugosr · 03-19-2020, 07:44 AM

Quote:

It's your job to find out why name resolution fails

Actually im new to Dockers and containers and facing the issue.
I tied my best to find the resolution but nothing works, that's why i requested help here.

berndbausch · 03-19-2020, 07:58 AM

I don't know if it has anything to do with Docker. First rule out that it is a network problem independent of Docker:

Is there basic connectivity to the nameserver?
Do programs like nslookup resolve the name using the nameserver?
Are you successful with a different nameserver?

venugosr · 03-19-2020, 08:47 AM

Hi,

Code:

[docker@dockernongui ~]$ cat /etc/resolv.conf
# Generated by NetworkManager
search server.com
nameserver 192.168.221.2
[docker@dockernongui ~]$

Here the 192.168.221.2 is the gateway of my Windows OS.

Code:

[docker@dockernongui ~]$ nslookup 192.168.221.2
** server can't find 2.221.168.192.in-addr.arpa: NXDOMAIN

[docker@dockernongui ~]$

Please find the below ip address from my Windows OS.

Quote:

Ethernet adapter VMware Network Adapter VMnet8:

Connection-specific DNS Suffix . :
IPv4 Address. . . . . . . . . . . : 192.168.221.1
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . :

but i can ping the 192.168.221.2

Code:

[docker@dockernongui ~]$ ping 192.168.221.2
PING 192.168.221.2 (192.168.221.2) 56(84) bytes of data.
64 bytes from 192.168.221.2: icmp_seq=1 ttl=128 time=0.600 ms
64 bytes from 192.168.221.2: icmp_seq=2 ttl=128 time=0.425 ms
64 bytes from 192.168.221.2: icmp_seq=3 ttl=128 time=0.369 ms
^C
--- 192.168.221.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 54ms
rtt min/avg/max/mdev = 0.369/0.464/0.600/0.101 ms
[docker@dockernongui ~]$

berndbausch · 03-19-2020, 09:09 AM

Can you resolve deb.debian.org using this nameserver?
- from within the container
- from the Centos VM that runs the container
- from the Windows host that runs the Centos VM
?

berndbausch · 03-19-2020, 09:12 AM

Quote:

Originally Posted by berndbausch

I don't know if it has anything to do with Docker. First rule out that it is a network problem independent of Docker:

Is there basic connectivity to the nameserver?
Do programs like nslookup resolve the name using the nameserver?
Are you successful with a different nameserver?

You have confirmed that there is basic connectivity. Not yet the two other questions.

venugosr · 03-19-2020, 09:22 AM

As i said earlier, i have tried all the possible ways to resolve the deb.debian.org error.
I have updated the /etc/resolv.conf by entering "namesever 8.8.8.8" and "nameserver 192.168.221.1", but nothing works.

My laptop is running on Windows 8.1
I have installed VMWare 14 version and installed CentOS 8
In CentOS i have installed the docker and container for my learning.

Code:

[docker@dockernongui ~]$ curl deb.debian.org
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
   <TITLE>Welcome to deb.debian.org (fastly instance)!</TITLE>
</HEAD>
<BODY>

<H1>Welcome to deb.debian.org (fastly instance)!</H1>

Quote:

Are you successful with a different nameserver?

No, i can't.

venugosr · 03-20-2020, 02:10 AM

Hi,

Could someone please help me how to set the Windows IP Address in Linux as i am using VMWare.