Add default DNS configuration properties

Sources/ContainerPersistence/ContainerSystemConfig.swift

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 import CVersion
+import ContainerResource
 import ContainerVersion
 import ContainerizationExtras
 import Foundation
@@ -132,15 +133,31 @@ final public class ContainerConfig: Codable, Sendable {
 }
 
 final public class DNSConfig: Codable, Sendable {
+    public let nameservers: [String]
     public let domain: String?
+    public let searchDomains: [String]
+    public let options: [String]
 
-    public init(domain: String? = nil) {
+    public init(
+        nameservers: [String] = ContainerConfiguration.DNSConfiguration.defaultNameservers,
+        domain: String? = nil,
+        searchDomains: [String] = [],
+        options: [String] = []
+    ) {
+        self.nameservers = nameservers
         self.domain = domain
+        self.searchDomains = searchDomains
+        self.options = options
     }
 
     public init(from decoder: any Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)
+        self.nameservers =
+            try container.decodeIfPresent([String].self, forKey: .nameservers)
+            ?? ContainerConfiguration.DNSConfiguration.defaultNameservers
         self.domain = try container.decodeIfPresent(String.self, forKey: .domain)
+        self.searchDomains = try container.decodeIfPresent([String].self, forKey: .searchDomains) ?? []
+        self.options = try container.decodeIfPresent([String].self, forKey: .options) ?? []
     }
 }
 

Sources/Services/ContainerAPIService/Client/Utility.swift

@@ -224,17 +224,11 @@ public struct Utility {
             }
         }
 
-        if management.dnsDisabled {
-            config.dns = nil
-        } else {
-            let domain = management.dns.domain ?? containerSystemConfig.dns.domain
-            config.dns = .init(
-                nameservers: management.dns.nameservers,
-                domain: domain,
-                searchDomains: management.dns.searchDomains,
-                options: management.dns.options
-            )
-        }
+        config.dns = dnsConfiguration(
+            dns: management.dns,
+            dnsDisabled: management.dnsDisabled,
+            defaults: containerSystemConfig.dns
+        )
 
         config.rosetta = management.rosetta || (Platform.current.architecture == "arm64" && requestedPlatform.architecture == "amd64")
 
@@ -272,6 +266,19 @@ public struct Utility {
         return (config, kernel, management.initImage)
     }
 
+    static func dnsConfiguration(dns: Flags.DNS, dnsDisabled: Bool, defaults: DNSConfig) -> ContainerConfiguration.DNSConfiguration? {
+        guard !dnsDisabled else {
+            return nil
+        }
+
+        return .init(
+            nameservers: dns.nameservers.isEmpty ? defaults.nameservers : dns.nameservers,
+            domain: dns.domain ?? defaults.domain,
+            searchDomains: dns.searchDomains.isEmpty ? defaults.searchDomains : dns.searchDomains,
+            options: dns.options.isEmpty ? defaults.options : dns.options
+        )
+    }
+
     static func getAttachmentConfigurations(
         containerId: String,
         builtinNetworkId: String?,

Tests/ContainerAPIClientTests/UtilityTests.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //===----------------------------------------------------------------------===//
 
+import ContainerPersistence
 import ContainerResource
 import ContainerizationError
 import Foundation
@@ -31,6 +32,53 @@ struct UtilityTests {
         #expect(result["key2"] == "value2")
     }
 
+    @Test("DNS config uses system defaults when CLI flags are absent")
+    func testDNSConfigurationUsesSystemDefaults() throws {
+        let defaults = DNSConfig(
+            nameservers: ["9.9.9.9", "149.112.112.112"],
+            domain: "containers.example",
+            searchDomains: ["svc.example"],
+            options: ["ndots:1"]
+        )
+
+        let dns = try #require(Utility.dnsConfiguration(dns: try Flags.DNS.parse([]), dnsDisabled: false, defaults: defaults))
+
+        #expect(dns.nameservers == ["9.9.9.9", "149.112.112.112"])
+        #expect(dns.domain == "containers.example")
+        #expect(dns.searchDomains == ["svc.example"])
+        #expect(dns.options == ["ndots:1"])
+    }
+
+    @Test("DNS CLI flags override system defaults")
+    func testDNSConfigurationCLIOverridesSystemDefaults() throws {
+        let defaults = DNSConfig(
+            nameservers: ["9.9.9.9"],
+            domain: "containers.example",
+            searchDomains: ["svc.example"],
+            options: ["ndots:1"]
+        )
+        let flags = Flags.DNS(
+            domain: "override.example",
+            nameservers: ["8.8.8.8"],
+            options: ["debug"],
+            searchDomains: ["override.search"]
+        )
+
+        let dns = try #require(Utility.dnsConfiguration(dns: flags, dnsDisabled: false, defaults: defaults))
+
+        #expect(dns.nameservers == ["8.8.8.8"])
+        #expect(dns.domain == "override.example")
+        #expect(dns.searchDomains == ["override.search"])
+        #expect(dns.options == ["debug"])
+    }
+
+    @Test("DNS config is disabled by no-dns")
+    func testDNSConfigurationDisabled() throws {
+        let dns = Utility.dnsConfiguration(dns: try Flags.DNS.parse([]), dnsDisabled: true, defaults: .init(nameservers: ["9.9.9.9"]))
+
+        #expect(dns == nil)
+    }
+
     @Test("Parse standalone keys")
     func testStandaloneKeys() {
         let result = Utility.parseKeyValuePairs(["standalone"])

Tests/ContainerPersistenceTests/ConfigurationLoaderTests.swift

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 import ContainerTestSupport
+import ContainerResource
 import ContainerizationExtras
 import Foundation
 import SystemPackage
@@ -90,7 +91,10 @@ struct ConfigurationLoaderTests {
             #expect(config.build.memory == BuildConfig.defaultMemory)
             #expect(config.container.cpus == 4)
             #expect(config.container.memory == ContainerConfig.defaultMemory)
+            #expect(config.dns.nameservers == ContainerConfiguration.DNSConfiguration.defaultNameservers)
             #expect(config.dns.domain == nil)
+            #expect(config.dns.searchDomains == [])
+            #expect(config.dns.options == [])
             #expect(!config.build.image.isEmpty)
             #expect(!config.vminit.image.isEmpty)
             #expect(!config.kernel.binaryPath.isEmpty)
@@ -115,7 +119,10 @@ struct ConfigurationLoaderTests {
                 memory = "8g"
 
                 [dns]
+                nameservers = ["8.8.8.8", "8.8.4.4"]
                 domain = "custom"
+                searchDomains = ["svc.local", "corp.local"]
+                options = ["ndots:1"]
 
                 [kernel]
                 binaryPath = "custom/path"
@@ -142,7 +149,10 @@ struct ConfigurationLoaderTests {
             #expect(config.container.cpus == 16)
             let expectedContainerMemory = try MemorySize("8g")
             #expect(config.container.memory == expectedContainerMemory)
+            #expect(config.dns.nameservers == ["8.8.8.8", "8.8.4.4"])
             #expect(config.dns.domain == "custom")
+            #expect(config.dns.searchDomains == ["svc.local", "corp.local"])
+            #expect(config.dns.options == ["ndots:1"])
             #expect(config.build.image == "custom-builder:latest")
             #expect(config.vminit.image == "custom-init:latest")
             #expect(config.kernel.binaryPath == "custom/path")

docs/container-system-config.md

@@ -14,7 +14,7 @@ Source of truth: [`Sources/ContainerPersistence/ContainerSystemConfig.swift`](..
 ```toml
 [build]      # builder VM resources and image
 [container]  # default per-container resources
-[dns]        # default DNS domain for DNS resolution on host
+[dns]        # default DNS settings for containers and host resolution
 [kernel]     # guest kernel binary path and download URL
 [network]    # default subnets for new networks
 [registry]   # default registry domain
@@ -46,9 +46,12 @@ Defaults applied when `container run` / `container create` is invoked without `-
 
 ## `[dns]`
 
-| Key      | Type      | Default | Description                                                                |
-|----------|-----------|---------|----------------------------------------------------------------------------|
-| `domain` | `String?` | unset   | Local DNS domain appended to container hostnames (e.g. `"test"` makes `my-web-server` resolvable as `my-web-server.test`). When unset, no domain is appended. |
+| Key             | Type       | Default       | Description                                                                |
+|-----------------|------------|---------------|----------------------------------------------------------------------------|
+| `nameservers`   | `[String]` | `["1.1.1.1"]` | DNS nameserver IP addresses configured in containers when `--dns` is not supplied. |
+| `domain`        | `String?`  | unset         | Local DNS domain appended to container hostnames (e.g. `"test"` makes `my-web-server` resolvable as `my-web-server.test`). When unset, no domain is appended. |
+| `searchDomains` | `[String]` | `[]`          | DNS search domains configured in containers when `--dns-search` is not supplied. |
+| `options`       | `[String]` | `[]`          | DNS resolver options configured in containers when `--dns-option` is not supplied. |
 
 ## `[kernel]`
 

docs/how-to.md

@@ -656,7 +656,10 @@ cpus = 4
 memory = "1gb"
 
 [dns]
+nameservers = ["1.1.1.1"]
 domain = "test"
+searchDomains = []
+options = []
 
 [kernel]
 binaryPath = "opt/kata/share/kata-containers/vmlinux-6.18.5-177"

docs/tutorials/container-system-config-tutorial.md

@@ -41,7 +41,10 @@ cpus = 8
 memory = "4g"
 
 [dns]
+nameservers = ["9.9.9.9", "149.112.112.112"]
 domain = "test"
+searchDomains = ["corp.example"]
+options = ["ndots:1"]
 ```
 
 Each top-level table maps directly to a section of [ContainerSystemConfig](../container-system-config.md).