feat: allows users to have more control on DNS (kubernetes-sigs#9270)

Signed-off-by: eminaktas <eminaktas34@gmail.com>

Signed-off-by: eminaktas <eminaktas34@gmail.com>

docs/dns-stack.md

@@ -19,13 +19,23 @@ ndots value to be used in ``/etc/resolv.conf``
 It is important to note that multiple search domains combined with high ``ndots``
 values lead to poor performance of DNS stack, so please choose it wisely.
 
+## dns_timeout
+
+timeout value to be used in ``/etc/resolv.conf``
+
+## dns_attempts
+
+attempts value to be used in ``/etc/resolv.conf``
+
 ### searchdomains
 
 Custom search domains to be added in addition to the cluster search domains (``default.svc.{{ dns_domain }}, svc.{{ dns_domain }}``).
 
 Most Linux systems limit the total number of search domains to 6 and the total length of all search domains
 to 256 characters. Depending on the length of ``dns_domain``, you're limited to less than the total limit.
 
+`remove_default_searchdomains: true` will remove the default cluster search domains.
+
 Please note that ``resolvconf_mode: docker_dns`` will automatically add your systems search domains as
 additional search domains. Please take this into the accounts for the limits.
 
@@ -270,7 +280,8 @@ nodelocaldns_secondary_skew_seconds: 5
 
 * the ``searchdomains`` have a limitation of a 6 names and 256 chars
   length. Due to default ``svc, default.svc`` subdomains, the actual
-  limits are a 4 names and 239 chars respectively.
+  limits are a 4 names and 239 chars respectively. If `remove_default_searchdomains: true`
+  added you are back to 6 names.
 
 * the ``nameservers`` have a limitation of a 3 servers, although there
   is a way to mitigate that with the ``upstream_dns_servers``,

docs/vars.md

@@ -28,6 +28,7 @@ Some variables of note include:
 * *kube_proxy_mode* - Changes k8s proxy mode to iptables mode
 * *kube_version* - Specify a given Kubernetes version
 * *searchdomains* - Array of DNS domains to search when looking up hostnames
+* *remove_default_searchdomains* - Boolean that removes the default searchdomain
 * *nameservers* - Array of nameservers to use for DNS lookup
 * *preinstall_selinux_state* - Set selinux state, permitted values are permissive, enforcing and disabled.
 
@@ -166,6 +167,7 @@ variables to match your requirements.
   addition to Kubespray deployed DNS
 * *nameservers* - Array of DNS servers configured for use by hosts
 * *searchdomains* - Array of up to 4 search domains
+* *remove_default_searchdomains* - Boolean. If enabled, `searchdomains` variable can hold 6 search domains.
 * *dns_etchosts* - Content of hosts file for coredns and nodelocaldns
 
 For more information, see [DNS

inventory/sample/group_vars/k8s_cluster/k8s-cluster.yml

@@ -160,6 +160,14 @@ kube_encrypt_secret_data: false
 cluster_name: cluster.local
 # Subdomains of DNS domain to be resolved via /etc/resolv.conf for hostnet pods
 ndots: 2
+# dns_timeout: 2
+# dns_attempts: 2
+# Custom search domains to be added in addition to the default cluster search domains
+# searchdomains:
+#   - svc.{{ cluster_name }}
+#   - default.svc.{{ cluster_name  }}
+# Remove default cluster search domains (``default.svc.{{ dns_domain }}, svc.{{ dns_domain }}``).
+# remove_default_searchdomains: false
 # Can be coredns, coredns_dual, manual or none
 dns_mode: coredns
 # Set manual server if using a custom cluster DNS server

roles/kubernetes/preinstall/tasks/0040-set_facts.yml

@@ -91,12 +91,17 @@
   changed_when: false
   check_mode: no
 
+- name: set default dns if remove_default_searchdomains is false
+  set_fact:
+    default_searchdomains: ["default.svc.{{ dns_domain }}", "svc.{{ dns_domain }}"]
+  when: not remove_default_searchdomains|default()|bool or (remove_default_searchdomains|default()|bool and searchdomains|default([])|length==0)
+
 - name: set dns facts
   set_fact:
     resolvconf: >-
       {%- if resolvconf.rc == 0 and resolvconfd_path.stat.isdir is defined and resolvconfd_path.stat.isdir -%}true{%- else -%}false{%- endif -%}
     bogus_domains: |-
-      {% for d in [ 'default.svc.' + dns_domain, 'svc.' + dns_domain ] + searchdomains|default([]) -%}
+      {% for d in default_searchdomains|default([]) + searchdomains|default([]) -%}
       {{ dns_domain }}.{{ d }}./{{ d }}.{{ d }}./com.{{ d }}./
       {%- endfor %}
     cloud_resolver: "{{ ['169.254.169.254'] if cloud_provider is defined and cloud_provider == 'gce' else
@@ -169,11 +174,11 @@
 - name: generate search domains to resolvconf
   set_fact:
     searchentries:
-      search {{ ([ 'default.svc.' + dns_domain, 'svc.' + dns_domain ] + searchdomains|default([])) | join(' ') }}
+      search {{ (default_searchdomains|default([]) + searchdomains|default([])) | join(' ') }}
     domainentry:
       domain {{ dns_domain }}
     supersede_search:
-      supersede domain-search "{{ ([ 'default.svc.' + dns_domain, 'svc.' + dns_domain ] + searchdomains|default([])) | join('", "') }}";
+      supersede domain-search "{{ (default_searchdomains|default([]) + searchdomains|default([])) | join('", "') }}";
     supersede_domain:
       supersede domain-name "{{ dns_domain }}";
 
@@ -196,7 +201,7 @@
 - name: generate nameservers for resolvconf, including cluster DNS
   set_fact:
     nameserverentries: |-
-      {{ ( ( [nodelocaldns_ip] if enable_nodelocaldns else []) + coredns_server|d([]) + nameservers|d([]) + cloud_resolver|d([]) + configured_nameservers|d([])) | unique | join(',') }}
+      {{ (([nodelocaldns_ip] if enable_nodelocaldns else []) + (coredns_server|d([]) if not enable_nodelocaldns else []) + nameservers|d([]) + cloud_resolver|d([]) + configured_nameservers|d([])) | unique | join(',') }}
     supersede_nameserver:
       supersede domain-name-servers {{ ( coredns_server|d([]) + nameservers|d([]) + cloud_resolver|d([])) | unique | join(', ') }};
   when: not dns_early or dns_late

roles/kubernetes/preinstall/tasks/0060-resolvconf.yml

@@ -13,9 +13,7 @@
       {% for item in nameserverentries.split(',') %}
       nameserver {{ item }}
       {% endfor %}
-      options ndots:{{ ndots }}
-      options timeout:2
-      options attempts:2
+      options ndots:{{ ndots }} timeout:{{ dns_timeout|default('2') }} attempts:{{ dns_attempts|default('2') }}
     state: present
     insertbefore: BOF
     create: yes

roles/kubernetes/preinstall/tasks/0063-networkmanager-dns.yml

@@ -9,12 +9,17 @@
     backup: yes
   notify: Preinstall | update resolvconf for networkmanager
 
+- name: set default dns if remove_default_searchdomains is false
+  set_fact:
+    default_searchdomains: ["default.svc.{{ dns_domain }}", "svc.{{ dns_domain }}"]
+  when: not remove_default_searchdomains|default()|bool or (remove_default_searchdomains|default()|bool and searchdomains|default([])|length==0)
+
 - name: NetworkManager | Add DNS search to NM configuration
   ini_file:
     path: /etc/NetworkManager/conf.d/dns.conf
     section: global-dns
     option: searches
-    value: "{{ ([ 'default.svc.' + dns_domain, 'svc.' + dns_domain ] + searchdomains|default([])) | join(',') }}"
+    value: "{{ (default_searchdomains|default([]) + searchdomains|default([])) | join(',') }}"
     mode: '0600'
     backup: yes
   notify: Preinstall | update resolvconf for networkmanager
@@ -24,7 +29,7 @@
     path: /etc/NetworkManager/conf.d/dns.conf
     section: global-dns
     option: options
-    value: "ndots:{{ ndots }};timeout:2;attempts:2;"
+    value: "ndots:{{ ndots }};timeout:{{ dns_timeout|default('2') }};attempts:{{ dns_attempts|default('2') }};"
     mode: '0600'
     backup: yes
   notify: Preinstall | update resolvconf for networkmanager

roles/kubernetes/preinstall/templates/dhclient_dnsupdate.sh.j2

@@ -6,7 +6,7 @@
 if [ $reason = "BOUND" ]; then
   if [ -n "$new_domain_search" -o -n "$new_domain_name_servers" ]; then
     RESOLV_CONF=$(cat /etc/resolv.conf | sed -r '/^options (timeout|attempts|ndots).*$/d')
-    OPTIONS="options timeout:2\noptions attempts:2\noptions ndots:{{ ndots }}"
+    OPTIONS="options timeout:{{ dns_timeout|default('2') }} attempts:{{ dns_attempts|default('2') }} ndots:{{ ndots }}"
 
     printf "%b\n" "$RESOLV_CONF\n$OPTIONS" > /etc/resolv.conf
   fi

roles/kubernetes/preinstall/templates/dhclient_dnsupdate_rh.sh.j2

@@ -6,7 +6,7 @@
 zdnsupdate_config() {
   if [ -n "$new_domain_search" -o -n "$new_domain_name_servers" ]; then
     RESOLV_CONF=$(cat /etc/resolv.conf | sed -r '/^options (timeout|attempts|ndots).*$/d')
-    OPTIONS="options timeout:2\noptions attempts:2\noptions ndots:{{ ndots }}"
+    OPTIONS="options timeout:{{ dns_timeout|default('2') }} attempts:{{ dns_attempts|default('2') }} ndots:{{ ndots }}"
 
     echo -e "$RESOLV_CONF\n$OPTIONS" > /etc/resolv.conf
   fi

roles/kubernetes/preinstall/templates/resolved.conf.j2

@@ -5,7 +5,11 @@
 DNS={{ ([nodelocaldns_ip] if enable_nodelocaldns else coredns_server )| list | join(' ') }}
 {% endif %}
 FallbackDNS={{ ( upstream_dns_servers|d([]) + nameservers|d([]) + cloud_resolver|d([])) | unique | join(' ') }}
+{% if remove_default_searchdomains is sameas false or (remove_default_searchdomains is sameas true and searchdomains|default([])|length==0)%}
 Domains={{ ([ 'default.svc.' + dns_domain, 'svc.' + dns_domain ] + searchdomains|default([])) | join(' ') }}
+{% else %}
+Domains={{ searchdomains|default([]) | join(' ') }}
+{% endif %}
 #LLMNR=no
 #MulticastDNS=no
 DNSSEC=no