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Krb5 Server - Docker Image

Krb5 Server

This is a gcavalcante8808/krb5-server image with MIT Kerberos v5 installed with Alpine as base image.

Daily Builds are available and linux/amd64 and linux/arm64 support.

Simple Usage

If you just want to create a Krb5 Server from scratch, just clone the repository and use docker compose to bring it up quickly:

    cd tmp
    git clone https://github.com/gcavalcante8808/docker-krb5-server.git
    cd docker-krb5-server
    docker compose up -d

By default, an anonymous volume will be created and mounted on /var/lib/krb5kdc but you can mount your own volume. Use the example bellow as a guide:

volumes:
    krb5kdc-data:

services:
   kdc:
     image: gcavalcante8808/krb5-server
     build: .
     restart: always
     ports:
      - "88:88"
      - "464:464"
      - "749:749"
     environment:
       KRB5_REALM: EXAMPLE.COM
       KRB5_KDC: localhost
     volumes:
      - krb5kdc-data:/var/lib/krb5kdc

Usage

You need to supply the following environment variables:

• KRB5_REALM (MANDATORY): Your KRB5 REALM name in Upper Case and DNS format, like EXAMPLE.COM;
• KRB5_KDC (MANDATORY): Your KRB5 KDC Address. It's recommended that you use a TXT Dns entry, but you can use localhost for a simple installation (if you use localhost you can't setup the KDC slaves later ...);
• KRB5_ADMINSERVER(OPTIONAL): If not provided will be the same value that was provided for KRB5_KDC;
• KRB5_PASS: KDB and admin password for the database. If you don't provide this value, one will be created and printed in the first time that container is started; write down this password, it is necessary to login with kadmin and unblock the kdb files.

With all this information, you can now run the container:

    docker run -d --name krb5-server -e KRB5_REALM=EXAMPLE.COM -e KRB5_KDC=localhost -e KRB5_PASS=mypass -p 88:88 -p 464:464 -p 749:749 gcavalcante8808/krb5-server

If you haven't provided the password, find it at the logs:

    docker logs krb5-server

To acquire a ticket from your new domain, create a krb5.conf on "/etc" with the following config:

[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true
 rdns = false
 default_realm = YOURREALM.FQDN
 
[realms]
 YOURREALM.FQDN = {
    kdc = localhost
    admin_server = localhost
 }

By default Kerberos client on Apple laptops is having troubles to connect to KDC with following error message:

kinit [email protected]
[email protected]'s password: 
kinit: krb5_get_init_creds: unable to reach any KDC in realm EXAMPLE.COM, tried 1 KDC

It happens because Kerberos client doesn't fall to TCP protocol to fix it, you have to change your krb5.conf file

[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true
 rdns = false
 default_realm = YOURREALM.FQDN
 
[realms]
 YOURREALM.FQDN = {
    kdc = tcp/localhost:88
    admin_server = tcp/localhost:749
 }

After that changes you can successfully run kinit command mentioned above

By Default just the user admin/admin@REALM is created; to test the setup, try to acquire the ticket with the following commands:

    kinit admin/[email protected] # Will prompt for the password provided or the generated.
    klist

The Default Kadmin policy allows all members inside /admin policy to do anything in your kerberos database(default to * perm); if you need a more simple user, you can create users with /service policy (which defaults to aci perm).

Note About Low Entropy and Kerberos Database Creation

If your container won't start properly and show a message like "Loading random data" for a couple minutes, it indicates that the system don't have enough entropy available to provide a secure cryptographic loop to the program.

In this case you can use rngd (will be necessary to restart the container after this):

    /sbin/rngd

You can use havaged as well, as we can see in the digitalOcean tutorial:

https://www.digitalocean.com/community/tutorials/how-to-setup-additional-entropy-for-cloud-servers-using-haveged

After this, you just need to restart your container and it is g-n-go.

Other Information

This container uses the Krb5-Server provided by the Alpine Team. Take a look at the alpine site to verify the available versions of the package.

For more information on how to configure the clients or even the server take a loot at the MIT Krb5 Documentation.

Check the issues page at github if you want to contribute or profile a bug/request/enhancement.

Running Tests

There are a set of tests (written in python) available on the tests directory.

You run can the tests by running make run-tests-on-docker command.

Note: By Default, it requires docker/docker-compose and make installed and working.