Add router config validate subcommand

.changesets/feat_feature_configvalidatesubcommand.md

@@ -0,0 +1,9 @@
+### Add router config validate subcommand ([PR #6131](https://github.com/apollographql/router/pull/6131))
+
+Added new `router config validate` subcommand to allow validation of a Router config file without fully starting up the Router.
+
+```
+./router config validate <path-to-config-file.yaml>
+```
+
+By [@andrewmcgivery](https://github.com/andrewmcgivery) in https://github.com/apollographql/router/pull/6131

apollo-router/src/configuration/mod.rs

@@ -40,9 +40,10 @@ use self::expansion::Expansion;
 pub(crate) use self::experimental::Discussed;
 pub(crate) use self::schema::generate_config_schema;
 pub(crate) use self::schema::generate_upgrade;
+pub(crate) use self::schema::validate_yaml_configuration;
+pub(crate) use self::schema::Mode;
 use self::subgraph::SubgraphConfiguration;
 use crate::cache::DEFAULT_CACHE_CAPACITY;
-use crate::configuration::schema::Mode;
 use crate::graphql;
 use crate::notification::Notify;
 use crate::plugin::plugins;

apollo-router/src/configuration/schema.rs

@@ -79,9 +79,6 @@ pub(crate) fn generate_config_schema() -> RootSchema {
 #[derive(Eq, PartialEq)]
 pub(crate) enum Mode {
     Upgrade,
-
-    // This is used only in testing to ensure that we don't allow old config in our tests.
-    #[cfg(test)]
     NoUpgrade,
 }
 

apollo-router/src/executable.rs

@@ -25,9 +25,12 @@ use regex::Regex;
 use url::ParseError;
 use url::Url;
 
+use crate::configuration::expansion::Expansion;
 use crate::configuration::generate_config_schema;
 use crate::configuration::generate_upgrade;
+use crate::configuration::validate_yaml_configuration;
 use crate::configuration::Discussed;
+use crate::configuration::Mode;
 use crate::metrics::meter_provider;
 use crate::plugin::plugins;
 use crate::plugins::telemetry::reload::init_telemetry;
@@ -142,6 +145,14 @@ enum ConfigSubcommand {
         #[clap(action = ArgAction::SetTrue, long)]
         diff: bool,
     },
+
+    /// Validate existing Router configuration file
+    Validate {
+        /// The location of the config to validate.
+        #[clap(value_parser, env = "APOLLO_ROUTER_CONFIG_PATH")]
+        config_path: PathBuf,
+    },
+
     /// List all the available experimental configurations with related GitHub discussion
     Experimental,
     /// List all the available preview configurations with related GitHub discussion
@@ -432,6 +443,21 @@ impl Executable {
                 println!("{}", serde_json::to_string_pretty(&schema)?);
                 Ok(())
             }
+            Some(Commands::Config(ConfigSubcommandArgs {
+                command: ConfigSubcommand::Validate { config_path },
+            })) => {
+                let config_string = std::fs::read_to_string(config_path)?;
+                validate_yaml_configuration(
+                    &config_string,
+                    Expansion::default()?,
+                    Mode::NoUpgrade,
+                )?
+                .validate()?;
+
+                println!("Configuration at path {:?} is valid!", config_path);
+
+                Ok(())
+            }
             Some(Commands::Config(ConfigSubcommandArgs {
                 command: ConfigSubcommand::Upgrade { config_path, diff },
             })) => {

docs/source/reference/router/configuration.mdx

@@ -347,6 +347,7 @@ GraphOS Router and Apollo Router Core provide a set of subcommands for interacti
 ```
 ./router config schema
 ./router config upgrade <path-to-config-file.yaml>
+./router config validate <path-to-config-file.yaml>
 ```
 
 <table class="field-table api-ref">
@@ -389,6 +390,21 @@ For details, see [Upgrading your router configuration](#upgrading-your-router-co
 </td>
 </tr>
 
+<tr>
+<td>
+
+##### `validate`
+
+</td>
+<td>
+
+Takes a config file and validates it against the router's full supported configuration format.
+
+Note: This is a static validation that checks if it is syntactically correct using the JSON schema. The router does additional logical checks on startup against the config that this command does not capture.
+
+</td>
+</tr>
+
 </tbody>
 </table>