如何在带有Linux的Azure App Services中使用自定义DNS服务器？

Question

I have a .NET Core API App running in Azure App Services using Windows, but now I want to test it using Linux. The app uses a custom DNS Zone just to map a custom hostname to a specific IP address.

To implement that in my Windows App Service I used the following Application Settings as stated in this page : WEBSITE_DNS_SERVER and WEBSITE_ALT_DNS_SERVER . Although it looks like a workaround, it works pretty well with Windows App Services. But in Linux it seems to have no effect and my app is not resolving the hostname as needed.

How can I use a custom DNS server in Azure App Service with Linux or add a custom hostname like editing the hosts file?

Answer 1

Unlike our App Service Windows, nameresolver.exe is not available and the Application settings for "WEBSITES_ALT_DNS" and "WEBSITES_DNS" do not populate the configuration files within the container. Below are steps are troubleshooting issues for "Alpine" based images since you don't mention if you are using a Linux container or the default Linux OS.

Install Bind-tools-

1. apk update
2. apk add bind-tools

Run Nslookup-

Once bind-tools is installed, you'll see the server that is being used. If bind-tools are not installed, the DNS server will not be shown. Example provided below.

 9031977be93a:~# nslookup google.com Server: 127.0.0.11 Address: 127.0.0.11#53 Non-authoritative answer: Name: google.com Address: 216.58.194.174 Name: google.com Address: 2607:f8b0:4005:801::200e 

Update Config file-

To use a different DNS server for testing, update the /etc/resolv.conf file and update the "nameserver" to use a different DNS server. In this example, we're using Googles DNS.

1. vi /etc/resolv.conf
2. By default, the following will be in the resolv.conf file.

search reddog.microsoft.com nameserver 127.0.0.11 options timeout:1 attempts:5 ndots:0cd /etc

3. If you're not familiar with "vi", press "i" on your keyboard to begin editing the file.
4. Once you're done, press "esc" and ":wq!" then enter.

search reddog.microsoft.com nameserver 8.8.8.8 options timeout:1 attempts:5 ndots:0

5. Running Nslookup again, you'll see the new nameserver being used.

 9031977be93a:~# nslookup google.com Server: 8.8.8.8 Address: 8.8.8.8#53 Non-authoritative answer: Name: google.com Address: 216.58.194.174 Name: google.com Address: 2607:f8b0:4005:804::200e 

Hardcoding Hostname-

You can also hardcode the IP address for the hostname in question for testing. To do so, you'll need to update the following file.

1. vi /etc/hosts
2. Add the IP address that you would like the DNS to point to. In this example, I'm changing the IP for my custom domain.

 127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters 172.20.0.2 9031977be93a 10.10.10.10 www.polytechniks.com 

3. Save the changes and use "ping" or "traceroute" to see the IP being used. NOTE: Nslookup does NOT use the /etc/hosts file so you will still see the IP address associated with the DNS.

 9031977be93a:~# ping www.polytechniks.com PING www.polytechniks.com (10.10.10.10): 56 data bytes --- www.polytechniks.com ping statistics --- 8 packets transmitted, 0 packets received, 100% packet loss 9031977be93a:~# traceroute www.polytechniks.com traceroute to www.polytechniks.com (10.10.10.10), 30 hops max, 46 byte packets 1 172.20.0.1 (172.20.0.1) 0.005 ms 0.004 ms 0.004 ms