kerberos-kdc: role to manage Kerberos KDC servers

This adds a role and related testing to manage our Kerberos KDC
servers, intended to replace the puppet modules currently performing
this task.

This role automates realm creation, initial setup, key material
distribution and replica host configuration.  None of this is intended
to run on the production servers which are already setup with an
active database, and the role should be effectively idempotent in
production.

Note that this does not yet switch the production servers into the new
groups; this can be done in a separate step under controlled
conditions and with related upgrades of the host OS to Focal.

Change-Id: I60b40897486b29beafc76025790c501b5055313d

doc/source/kerberos.rst

@@ -15,9 +15,8 @@ At a Glance
 
 :Hosts:
   * kdc*.openstack.org
-:Puppet:
-  * https://opendev.org/opendev/puppet-kerberos
-  * :git_file:`modules/openstack_project/manifests/kdc.pp`
+:Ansible:
+  * :git_file:`playbooks/service-kerberos.yaml`
 :Projects:
   * http://web.mit.edu/kerberos
 :Bugs:
@@ -30,50 +29,59 @@ At a Glance
 OpenStack Realm
 ---------------
 
-OpenStack runs a Kerberos ``Realm`` called ``OPENSTACK.ORG``.
-The realm contains a ``Key Distribution Center`` or KDC which is spread
-across a master and a slave, as well as an admin server which only runs on the
-master. Most of the configuration is in puppet, but initial setup and
-the management of user accounts, known as ``principals``, are manual tasks.
+OpenStack runs a Kerberos ``Realm`` called ``OPENSTACK.ORG``.  The
+realm contains a ``Key Distribution Center`` or KDC which is spread
+across a primary and a replica, as well as an admin server which only
+runs on the primary.
+
+Most of the configuration is in Ansible, but management of user
+accounts, known as ``principals``, is a manual task for
+administrators.
 
 Realm Creation
 --------------
 
-On the first KDC host, the admin needs to run `krb5_newrealm` by hand. Then
-admin principals and host principles need to be set up.
+Realm creation is exercised by the Ansible roles during testing, but
+is not expected to be used in production (because we have an active
+realm/database).
 
-Set up host principals for slave propagation::
+The general process is:
 
-   # execute kadmin.local then run these commands
-   addprinc -randkey host/kdc03.openstack.org
-   addprinc -randkey host/kdc04.openstack.org
-   ktadd host/kdc03.openstack.org
-   ktadd host/kdc04.openstack.org
+ * create the new Kerberos database on the primary
+ * distribute the database ``stash`` file from the primary to
+   replicas, to allow them to unencrypt the database propogated to
+   them.  This is created from a master key kept as a secret.
+ * create an admin user (password saved in file on primary server)
+ * add host principals for the primary and replica servers
+ * create keytabs on primary and replica servers (via the admin user),
+   which allows them to authenticate to each other.
+ * setup database propogation from primary to replicas with ``kprop``
+   (primary-side push) and ``kpropod`` (replica-side listen).
 
-Copy the file `/etc/krb5.keytab` to the second kdc host.
-
-The puppet config sets up slave propagation scripts and cron jobs to run them.
-
-You will also need to create a stash file after creating a new realm. Run
-`krb5_util stash` on the first kdc host. Copy the file `/etc/krb5kdc/stash`
-to all other KDC servers for the krb5-kdc daemons to run.
+In a disaster recovery situation, we can provision a fresh realm and
+recover principals from dump files (XXX: 2020-03-11 ianw -- dump file
+backup to come).
 
 .. _addprinc:
 
 Adding A User Principal
 -----------------------
 
-First, ensure the user has an entry in puppet so they have a unix
+First, ensure the user has an entry in Ansible so they have a Unix
 shell account on our hosts.  SSH access is not necessary, but keeping
 track of usernames and uids with account entries is necessary.
 
-Then, add the user to Kerberos using kadmin (while authenticated as a
-kerberos admin) or kadmin.local on the kdc::
+If you are already an admin, you should authenicate with ``kinit
+<username>/admin``.  Otherwise you can use the ``kadmin.local`` tool
+(instead of ``kadmin``) on the primary server, which by-passes
+authenication and writes to the database directly.
+
+Use ``kadmin`` to add the principal like so:
 
   kadmin: addprinc $USERNAME@OPENSTACK.ORG
 
 Where `$USERNAME` is the lower-case username of their unix account in
-puppet.  `OPENSTACK.ORG` should be capitalized.
+Ansible.  `OPENSTACK.ORG` should be capitalized.
 
 If you are adding an admin principal, use
 `username/admin@OPENSTACK.ORG`.  Admins should additionally have
@@ -87,11 +95,11 @@ than a person.  There is no difference in their implementation, only
 in conventions around how they are created and used.  Service
 principals are created without passwords and keytab files are used
 instead for authentication.  The program `k5start` can use keytab
-files to automatically obtain kerberos credentials (and AFS if
+files to automatically obtain Kerberos credentials (and AFS if
 needed).
 
 Add the service principal to Kerberos using kadmin (while
-authenticated as a kerberos admin) or kadmin.local on the kdc::
+authenticated as a Kerberos admin) or kadmin.local on the kdc::
 
   kadmin: addprinc -randkey service/$NAME@OPENSTACK.ORG
 
@@ -105,6 +113,10 @@ Then save the principal's keytab::
 .. warning:: Each time ``ktadd`` is run, the key is rotated and
              previous keytabs are invalidated.
 
+These keytabs are then usually converted to base-64 and stored as
+secret variables, and deployed to hosts via Ansible.
+``mirror-update`` is probably a good example.
+
 Resetting A User Principal's Password
 -------------------------------------
 
@@ -117,12 +129,12 @@ twice as prompted. If you need to reset your admin principal, use
 No Service Outage Server Maintenance
 ------------------------------------
 
-Should you need perform maintenance on the kerberos server that requires
-taking kerberos processes offline you can do this by performing your
+Should you need perform maintenance on the Kerberos server that requires
+taking Kerberos processes offline you can do this by performing your
 updates on a single server at a time.
 
 `kdc03.openstack.org` is our primary server and `kdc04.openstack.org`
-is the hot standby. Perform your maintenance on `kdc04.openstack.org`
+is the replica. Perform your maintenance on `kdc04.openstack.org`
 first. Then once that is done we can prepare for taking down the
 primary. On `kdc03.openstack.org` run::
 
@@ -132,7 +144,7 @@ You should see::
 
   Database propagation to kdc04.openstack.org: SUCCEEDED
 
-Once this is done the standby server is ready and we can take kdc03
+Once this is done the replica is ready and we can take kdc03
 offline. When kdc03 is back online rerun `run-kprop.sh` to ensure
 everything is working again.
 

inventory/service/group_vars/kerberos-kdc.yaml

@@ -0,0 +1,9 @@
+iptables_extra_public_tcp_ports:
+  - 88
+  - 464
+  - 749
+  - 754
+iptables_extra_public_udp_ports:
+  - 88
+  - 464
+  - 749

playbooks/roles/kerberos-kdc/README.rst

@@ -0,0 +1,27 @@
+Configure a Kerberos KDC server
+
+All KDC servers (primary and replicas) should be in a common
+``kerberos-kdc`` group that defines ``kerberos_kdc_realm`` and
+``kerberos_kdc_master_key``.
+
+The ``kerberos-kdc-primary`` group should have a single primary KDC
+host.  It will be configured to replicate its database to hosts in
+the ``kerberos-kdc-replica`` group.
+
+Hosts in the ``kerberos-kdc-replica`` group will be configured to
+receive updates from the ``kerberos-kdc-primary`` host.
+
+The role should be run twice; once limited to the primary group and
+then a second time limited to the secondary group.
+
+**Role Variables**
+
+
+.. zuul:rolevar:: kerberos_kdc_relam
+
+   The realm for all KDC servers.
+
+.. zuul:rolevar:: kerberos_kdc_master_key
+
+   The master key written into the *stash* file for each KDC, which
+   allows them to auth.

playbooks/roles/kerberos-kdc/files/kadm5.acl

@@ -0,0 +1,6 @@
+# This file Is the access control list for krb5 administration.
+# When this file is edited run /etc/init.d/krb5-admin-server restart to activate
+# One common way to set up Kerberos administration is to allow any principal
+# ending in /admin  is given full administrative rights.
+# To enable this, uncomment the following line:
+*/admin *

playbooks/roles/kerberos-kdc/files/krb5-kpropd.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Kerberos 5 replica KDC update server
+
+[Service]
+ExecReload=/bin/kill -HUP $MAINPID
+EnvironmentFile=-/etc/default/krb5-kpropd
+ExecStart=/usr/sbin/kpropd -D $DAEMON_ARGS
+InaccessibleDirectories=/etc/ssh /etc/ssl/private  /root
+ReadOnlyDirectories=/
+ReadWriteDirectories=/var/tmp /tmp /var/lib/krb5kdc /var/run /run
+CapabilityBoundingSet=CAP_NET_BIND_SERVICE
+
+[Install]
+WantedBy=multi-user.target

playbooks/roles/kerberos-kdc/tasks/main.yaml

@@ -0,0 +1,32 @@
+- name: Install packages
+  package:
+    name:
+      - krb5-kdc
+    state: present
+
+- name: Ensure directories
+  file:
+    path: '{{ item }}'
+    state: directory
+    mode: 0755
+    owner: root
+    group: root
+  loop:
+    - /etc/krb5kdc
+    - /var/krb5kdc
+
+- name: Install KDC config
+  template:
+    src: 'kdc.conf.j2'
+    dest: '/etc/krb5kdc/kdc.conf'
+    mode: 0644
+    owner: root
+    group: root
+
+- name: Copy kadm5.acl
+  copy:
+    src: kadm5.acl
+    dest: '/etc/krb5kdc/kadm5.acl'
+    mode: 0644
+    owner: root
+    group: root

playbooks/roles/kerberos-kdc/tasks/primary.yaml

@@ -0,0 +1,94 @@
+- name: Install packages
+  package:
+    name:
+      - krb5-admin-server
+    state: present
+
+# Note the following is not really for production, where we already
+# have a database setup.  It is exercsied by testing however.
+- name: Look for primary database
+  stat:
+    path: /var/lib/krb5kdc/principal
+  register: _db_created
+
+- name: Setup clean primary
+  when: not _db_created.stat.exists
+  block:
+
+    - name: Setup primary db
+      shell: |
+          yes {{ kerberos_kdc_master_key }} | kdb5_util create -r {{ kerberos_kdc_realm }} -s
+
+    - name: Generate and save admin principal password
+      copy:
+        dest: '/etc/krb5kdc/admin.passwd'
+        content: '{{ lookup("password", "/dev/null chars=ascii_letters,digits length=12") }}'
+        owner: root
+        group: root
+        mode: '0600'
+
+    - name: Setup initial admin principal
+      shell: |
+          echo "addprinc -pw $(cat /etc/krb5kdc/admin.passwd) admin/admin@{{ kerberos_kdc_realm }}" | kadmin.local
+
+    # https://web.mit.edu/kerberos/krb5-latest/doc/admin/install_kdc.html
+    #   It is not strictly necessary to have the primary KDC server in
+    #   the Kerberos database, but it can be handy if you want to be
+    #   able to swap the primary KDC with one of the replicas.
+    - name: Create primary host principal and keytab
+      shell:
+        cmd: |
+          echo "addprinc -randkey host/{{ inventory_hostname }}" | kadmin.local
+          echo "ktadd host/{{ inventory_hostname }}" | kadmin.local
+
+    - name: Create replica host principals
+      shell:
+        cmd: 'echo "addprinc -randkey host/{{ item }}" | kadmin.local'
+      with_inventory_hostnames: kerberos-kdc-replica
+
+# The stash file is used to decrypt the on-disk database.  Without
+# this you are prompted for the master password on daemon start.  This
+# needs to be distributed to the replicas so they can also open the
+# database.
+- name: Read and save stash file
+  slurp:
+    src: '/etc/krb5kdc/stash'
+  register: kerberos_kdc_stash_file_contents
+
+# Export this so replica servers can use this variable to authenicate
+# and create keytabs for their host principals, if they need to.
+- name: Read in admin/admin password
+  slurp:
+    src: "/etc/krb5kdc/admin.passwd"
+  register: _admin_password
+- name: Export admin password
+  set_fact:
+    kerberos_kdc_admin_password: '{{ _admin_password.content | b64decode }}'
+
+# kprop is what pushes the db to replicas.  Set it up to run via cron
+# periodically.
+- name: Install kprop script
+  template:
+    src: 'run-kprop.sh.j2'
+    dest: '/usr/local/bin/run-kprop.sh'
+    mode: 0755
+    owner: root
+    group: root
+
+- name: kprop cron to push db to replicas
+  cron:
+    name: kprop
+    minute: 15
+    job: '/usr/local/bin/run-kprop.sh >/dev/null 2>&1'
+
+- name: start krb5-admin-server
+  systemd:
+    state: started
+    enabled: yes
+    name: krb5-admin-server
+
+- name: start krb5-kdc
+  systemd:
+    state: started
+    enabled: yes
+    name: krb5-kdc

playbooks/roles/kerberos-kdc/tasks/replica.yaml

@@ -0,0 +1,64 @@
+- name: Install packages
+  package:
+    name:
+      - krb5-kdc
+      - krb5-kpropd
+    state: present
+
+# This is the key to unencrypt the database pushed by the primary
+- name: Install stash file from primary
+  shell:
+    cmd: 'echo "{{ hostvars[groups["kerberos-kdc-primary"][0]]["kerberos_kdc_stash_file_contents"].content }}" | base64 -d > /etc/krb5kdc/stash'
+    creates: '/etc/krb5kdc/stash'
+
+- name: Ensure stash file permsissions
+  file:
+    path: /etc/krb5kdc/stash
+    owner: root
+    group: root
+    mode: '0600'
+
+# Use the admin user to write out our host keytab
+- name: Create host keytab
+  shell:
+    cmd: |
+        echo "ktadd host/{{ inventory_hostname }}" | kadmin -p admin/admin -w '{{ hostvars[groups["kerberos-kdc-primary"][0]]["kerberos_kdc_admin_password"] }}'
+    creates: '/etc/krb5.keytab'
+
+# This specifies servers that are allowed to send us updates;
+# i.e. the primary server
+- name: Install kpropd ACL
+  template:
+    src: 'kpropd.acl.j2'
+    dest: '/etc/krb5kdc/kpropd.acl'
+    mode: 0644
+    owner: root
+    group: root
+
+- name: Install kpropd service
+  copy:
+    src: krb5-kpropd.service
+    dest: /etc/systemd/system/krb5-kpropd.service
+    mode: 0644
+    owner: root
+    group: root
+  register: _kpropd_service_installed
+
+- name: Reload systemd
+  systemd:
+    daemon_reload: yes
+  when: _kpropd_service_installed.changed
+
+- name: Ensure kpropd running
+  systemd:
+    state: started
+    name: krb5-kpropd
+    enabled: yes
+
+# Note we can't start until replicas are distributed; the main
+# service-kerberos.yaml playbook handles this.
+- name: Ensure krb5-kdc is enabled
+  systemd:
+    name: krb5-kdc
+    enabled: yes
+    masked: no

playbooks/roles/kerberos-kdc/templates/kdc.conf.j2

@@ -0,0 +1,16 @@
+[kdcdefaults]
+    kdc_ports = 750,88
+
+[realms]
+    {{ kerberos_kdc_realm }} = {
+        database_name = /var/lib/krb5kdc/principal
+        admin_keytab = FILE:/etc/krb5kdc/kadm5.keytab
+        acl_file = /etc/krb5kdc/kadm5.acl
+        key_stash_file = /etc/krb5kdc/stash
+        kdc_ports = 750,88
+        max_life = 10h 0m 0s
+        max_renewable_life = 7d 0h 0m 0s
+        master_key_type = aes256-cts
+        supported_enctypes = aes256-cts:normal
+        default_principal_flags = +preauth
+    }

playbooks/roles/kerberos-kdc/templates/kpropd.acl.j2

@@ -0,0 +1,3 @@
+{% for kdc in groups["kerberos-kdc-primary"] %}
+host/{{ kdc }}@{{ kerberos_kdc_realm }}
+{% endfor %}

playbooks/roles/kerberos-kdc/templates/run-kprop.sh.j2

@@ -0,0 +1,7 @@
+#!/bin/sh
+kdclist="{% for s in groups['kerberos-kdc-replica'] %}{{ s }} {% endfor %}"
+kdb5_util dump /var/krb5kdc/slave_datatrans
+for kdc in $kdclist
+do
+    kprop -f /var/krb5kdc/slave_datatrans $kdc
+done

playbooks/service-kerberos.yaml

@@ -0,0 +1,47 @@
+# Setting up a fresh realm, as done in CI, is a five step process of:
+#
+#  1. setup common packages/config
+#  2. setup primary; create db, setup kprop pushes, start services.
+#  3. configure replica to accept db updates via kpropd
+#  4. do a db replication
+#  5. start replica daemons now they have a db copy
+#
+# In production this is largely a no-op just ensuring things are
+# running.
+
+- hosts: "kerberos-kdc:!disabled"
+  name: "Configure common KDC components"
+  roles:
+    - kerberos-client
+    - kerberos-kdc
+
+- hosts: "kerberos-kdc-primary:!disabled"
+  name: "Configure Kerberos Primary"
+  tasks:
+    - name: Configure primary KDC
+      include_role:
+        name: kerberos-kdc
+        tasks_from: primary
+
+- hosts: "kerberos-kdc-replica:!disabled"
+  name: "Configure Kerberos Replicas"
+  tasks:
+    - name: Configure replica KDC
+      include_role:
+        name: kerberos-kdc
+        tasks_from: replica
+
+- hosts: "kerberos-kdc-primary:!disabled"
+  name: "Run replication"
+  tasks:
+    - name: Run a DB replication
+      shell: |
+        /usr/local/bin/run-kprop.sh
+
+- hosts: "kerberos-kdc-replica:!disabled"
+  name: "Ensure krb5-kdc running"
+  tasks:
+    - name: Start krb5-kdc
+      systemd:
+        name: krb5-kdc
+        state: started

playbooks/test-kerberos.yaml

@@ -0,0 +1,7 @@
+- hosts: "kdc-primary.opendev.org"
+  tasks:
+
+    - name: Run kinit
+      shell: |
+        cat /etc/krb5kdc/admin.passwd | kinit admin/admin
+

playbooks/zuul/run-base.yaml

@@ -58,6 +58,7 @@
         - group_vars/registry.yaml
         - group_vars/gitea.yaml
         - group_vars/gitea-lb.yaml
+        - group_vars/kerberos-kdc.yaml
         - group_vars/letsencrypt.yaml
         - group_vars/meetpad.yaml
         - group_vars/jvb.yaml

playbooks/zuul/templates/gate-groups.yaml.j2

@@ -27,3 +27,11 @@ groups:
   borg-backup:
     - borg-backup-test01.opendev.org
     - borg-backup-test02.opendev.org
+
+  kerberos-kdc:
+    - kdc-primary.opendev.org
+    - kdc-replica.opendev.org
+  kerberos-kdc-primary:
+    - kdc-primary.opendev.org
+  kerberos-kdc-replica:
+    - kdc-replica.opendev.org

playbooks/zuul/templates/group_vars/kerberos-kdc.yaml.j2

@@ -0,0 +1,10 @@
+# global server settings
+kerberos_kdc_realm: OPENDEV.CI
+kerberos_kdc_master_key: masterkey123
+
+# client settings
+kerberos_realm: OPENDEV.CI
+kerberos_admin_server: kdc-primary.opendev.org
+kerberos_kdcs:
+  - kdc-primary.opendev.org
+  - kdc-replica.opendev.org

zuul.d/infra-prod.yaml

@@ -593,6 +593,23 @@
       - modules/
       - manifests/
 
+- job:
+    name: infra-prod-service-kerberos
+    parent: infra-prod-service-base
+    description: Run Kerberos playbook.
+    vars:
+      playbook_name: service-kerberos.yaml
+      infra_prod_ansible_forks: 1
+    required-projects:
+      - opendev/system-config
+    files:
+      - inventory/
+      - playbooks/service-kerberos.yaml
+      - inventory/service/group_vars/kerberos-kdc.yaml
+      - playbooks/roles/kerberos-kdc/
+      - roles/kerberos-client/
+      - playbooks/roles/iptables/
+
 - job:
     name: infra-prod-remote-puppet-else
     parent: infra-prod-service-base

zuul.d/project.yaml

@@ -25,6 +25,7 @@
               - name: opendev-buildset-registry
               - name: system-config-build-image-hound
                 soft: true
+        - system-config-run-kerberos
         - system-config-run-lists
         - system-config-run-nodepool
         - system-config-run-meetpad:
@@ -131,6 +132,7 @@
               - name: opendev-buildset-registry
               - name: system-config-upload-image-hound
                 soft: true
+        - system-config-run-kerberos
         - system-config-run-lists
         - system-config-run-nodepool
         - system-config-run-meetpad:
@@ -253,6 +255,7 @@
                 soft: true
         - infra-prod-service-bridge
         - infra-prod-service-gitea-lb
+        - infra-prod-service-kerberos
         - infra-prod-service-nameserver
         - infra-prod-service-nodepool
         - infra-prod-service-codesearch:
@@ -320,6 +323,7 @@
         - infra-prod-service-nameserver
         - infra-prod-service-etherpad
         - infra-prod-service-meetpad
+        - infra-prod-service-kerberos
         - infra-prod-service-mirror-update
         - infra-prod-service-mirror
         - infra-prod-service-static

zuul.d/system-config-run.yaml

@@ -919,3 +919,35 @@
       - testinfra/test_refstack.py
       # If we rebuild the image, we want to run this job as well.
       - docker/refstack/.*
+
+- job:
+    name: system-config-run-kerberos
+    parent: system-config-run
+    ansible-version: 2.9
+    description: |
+      Run the playbook for kerberos servers
+    timeout: 3600
+    nodeset:
+      nodes:
+        - name: bridge.openstack.org
+          label: ubuntu-bionic
+        - name: kdc-primary.opendev.org
+          label: ubuntu-focal
+        - name: kdc-replica.opendev.org
+          label: ubuntu-focal
+    host-vars:
+      kdc-primary.opendev.org:
+        host_copy_output:
+          '/etc/krb5kdc/': logs
+          '/var/krb5kdc/': logs
+      kdc-replica.opendev.org:
+        host_copy_output:
+          '/etc/krb5kdc/': logs
+          '/var/krb5kdc/': logs
+    vars:
+      run_playbooks:
+        - playbooks/service-kerberos.yaml
+      run_test_playbook: playbooks/test-kerberos.yaml
+    files:
+      - playbooks/bridge.yaml
+      - playbooks/roles/kerberos-kdc/