[dns] Implement config and show commands for static DNS. (sonic-net#2737)

- What I did
Implement config and show commands for static DNS feature. According to sonic-net/SONiC#1262 HLD.

- How I did it
Static DNS config commands are implemented in the new config/dns.py file. DNS config commands are available under config dns ... sub-command.
Show commands are implemented in the new show/dns.py file. DNS show commands are available under show dns ... sub-command.

- How to verify it
Compile sonic-utilities package. The unit tests will run automatically during the compilation.
Coverage for config/dns.py : 94%
Coverage for show/dns.py : 86%

- Previous command output (if the output of a command-line utility has changed)

- New command output (if the output of a command-line utility has changed)
# config dns nameserver add 1.1.1.1
# config dns nameserver add 8.8.8.8
# show dns nameserver
  Nameserver
------------
     1.1.1.1
     8.8.8.8

Author: oleksandrivantsiv

config/dns.py

@@ -0,0 +1,96 @@
+
+import click
+from swsscommon.swsscommon import ConfigDBConnector
+from .validated_config_db_connector import ValidatedConfigDBConnector
+import ipaddress
+
+
+ADHOC_VALIDATION = True
+NAMESERVERS_MAX_NUM = 3
+
+
+def to_ip_address(address):
+    """Check if the given IP address is valid"""
+    try:
+        ip = ipaddress.ip_address(address)
+
+        if ADHOC_VALIDATION:
+            if ip.is_reserved or ip.is_multicast or ip.is_loopback:
+                return
+
+            invalid_ips = [
+                ipaddress.IPv4Address('0.0.0.0'),
+                ipaddress.IPv4Address('255.255.255.255'),
+                ipaddress.IPv6Address("0::0"),
+                ipaddress.IPv6Address("0::1")
+                ]
+            if ip in invalid_ips:
+                return
+
+        return ip
+    except Exception:
+        return
+
+
+def get_nameservers(db):
+    nameservers = db.get_table('DNS_NAMESERVER')
+    return [ipaddress.ip_address(ip) for ip in nameservers]
+
+
+# 'dns' group ('config dns ...')
+@click.group()
+@click.pass_context
+def dns(ctx):
+    """Static DNS configuration"""
+    config_db = ValidatedConfigDBConnector(ConfigDBConnector())
+    config_db.connect()
+    ctx.obj = {'db': config_db}
+
+
+# dns nameserver config
+@dns.group('nameserver')
+@click.pass_context
+def nameserver(ctx):
+    """Static DNS nameservers configuration"""
+    pass
+
+
+# dns nameserver add
+@nameserver.command('add')
+@click.argument('ip_address_str', metavar='<ip_address>', required=True)
+@click.pass_context
+def add_dns_nameserver(ctx, ip_address_str):
+    """Add static DNS nameserver entry"""
+    ip_address = to_ip_address(ip_address_str)
+    if not ip_address:
+        ctx.fail(f"{ip_address_str} invalid nameserver ip address")
+
+    db = ctx.obj['db']
+
+    nameservers = get_nameservers(db)
+    if ip_address in nameservers:
+        ctx.fail(f"{ip_address} nameserver is already configured")
+
+    if len(nameservers) >= NAMESERVERS_MAX_NUM:
+        ctx.fail(f"The maximum number ({NAMESERVERS_MAX_NUM}) of nameservers exceeded.")
+
+    db.set_entry('DNS_NAMESERVER', ip_address, {})
+
+# dns nameserver delete
+@nameserver.command('del')
+@click.argument('ip_address_str', metavar='<ip_address>', required=True)
+@click.pass_context
+def del_dns_nameserver(ctx, ip_address_str):
+    """Delete static DNS nameserver entry"""
+
+    ip_address = to_ip_address(ip_address_str)
+    if not ip_address:
+        ctx.fail(f"{ip_address_str} invalid nameserver ip address")
+
+    db = ctx.obj['db']
+
+    nameservers = get_nameservers(db)
+    if ip_address not in nameservers:
+        ctx.fail(f"DNS nameserver {ip_address} is not configured")
+
+    db.set_entry('DNS_NAMESERVER', ip_address, None)

config/main.py

@@ -56,6 +56,7 @@
 from .config_mgmt import ConfigMgmtDPB, ConfigMgmt
 from . import mclag
 from . import syslog
+from . import dns
 
 # mock masic APIs for unit test
 try:
@@ -1198,6 +1199,9 @@ def config(ctx):
 # syslog module
 config.add_command(syslog.syslog)
 
+# DNS module
+config.add_command(dns.dns)
+
 @config.command()
 @click.option('-y', '--yes', is_flag=True, callback=_abort_if_false,
                 expose_value=False, prompt='Existing files will be overwritten, continue?')

doc/Command-Reference.md

@@ -194,12 +194,15 @@
   * [MACsec config command](#macsec-config-command)
   * [MACsec show command](#macsec-show-command)
   * [MACsec clear command](#macsec-clear-command)
-
+* [Static DNS Commands](#static-dns-commands)
+  * [Static DNS config command](#static-dns-config-command)
+  * [Static DNS show command](#static-dns-show-command)
 
 ## Document History
 
 | Version | Modification Date | Details |
 | --- | --- | --- |
+| v7 | Jun-22-2023 | Add static DNS show and config commands |
 | v6 | May-06-2021 | Add SNMP show and config commands |
 | v5 | Nov-05-2020 | Add document for console commands |
 | v4 | Oct-17-2019 | Unify usage statements and other formatting; Replace tabs with spaces; Modify heading sizes; Fix spelling, grammar and other errors; Fix organization of new commands |
@@ -12442,3 +12445,55 @@ Clear MACsec counters which is to reset all MACsec counters to ZERO.
   ```
 
 Go Back To [Beginning of the document](#) or [Beginning of this section](#macsec-commands)
+
+# Static DNS Commands
+
+This sub-section explains the list of the configuration options available for static DNS feature.
+
+## Static DNS config command
+
+- Add static DNS nameserver entry
+
+```
+admin@sonic:~$ config dns nameserver add -h
+Usage: config dns nameserver add [OPTIONS] <ip_address>
+
+  Add static DNS nameserver entry
+
+Options:
+  -?, -h, --help  Show this message and exit.
+```
+
+- Delete static DNS nameserver entry
+
+```
+admin@sonic:~$ config dns nameserver del -h
+Usage: config dns nameserver del [OPTIONS] <ip_address>
+
+  Delete static DNS nameserver entry
+
+Options:
+  -h, -?, --help  Show this message and exit.
+```
+
+## Static DNS  show command
+
+- Show static DNS configuration
+
+```
+admin@sonic:~$ show dns nameserver -h
+Usage: show dns nameserver [OPTIONS]
+
+  Show static DNS configuration
+
+Options:
+  -h, -?, --help  Show this message and exit.
+```
+```
+admin@sonic:~$ show dns nameserver
+  Nameserver
+------------
+     1.1.1.1
+     8.8.8.8
+
+```

show/dns.py

@@ -0,0 +1,30 @@
+import click
+import utilities_common.cli as clicommon
+from natsort import natsorted
+from tabulate import tabulate
+
+from swsscommon.swsscommon import ConfigDBConnector
+from utilities_common.cli import pass_db
+
+
+# 'dns' group ("show dns ...")
+@click.group(cls=clicommon.AliasedGroup)
+@click.pass_context
+def dns(ctx):
+    """Show details of the static DNS configuration """
+    config_db = ConfigDBConnector()
+    config_db.connect()
+    ctx.obj = {'db': config_db}
+
+
+# 'nameserver' subcommand ("show dns nameserver")
+@dns.command()
+@click.pass_context
+def nameserver(ctx):
+    """ Show static DNS configuration """
+    header = ["Nameserver"]
+    db = ctx.obj['db']
+
+    nameservers = db.get_table('DNS_NAMESERVER')
+
+    click.echo(tabulate([(ns,) for ns in nameservers.keys()], header, tablefmt='simple', stralign='right'))

show/main.py

@@ -64,6 +64,7 @@
 from . import warm_restart
 from . import plugins
 from . import syslog
+from . import dns
 
 # Global Variables
 PLATFORM_JSON = 'platform.json'
@@ -295,6 +296,7 @@ def cli(ctx):
 cli.add_command(vxlan.vxlan)
 cli.add_command(system_health.system_health)
 cli.add_command(warm_restart.warm_restart)
+cli.add_command(dns.dns)
 
 # syslog module
 cli.add_command(syslog.syslog)