feat: add single zone configuration

Before this change, there was no way to set up a specific zone for EC2 instance.
This feature allows configuring a specific zone in Test.toml for a certain variant
when launching its EC2 instance(s). Even though a minimum of two zones are needed
when creating an EKS cluster, after the cluster is created this feature can limit
one specific zone before launching the EC2 instances.

Author: zongzhidanielhu

bottlerocket/agents/src/bin/ec2-resource-agent/ec2_provider.rs

@@ -235,8 +235,14 @@ where
     for instance_type in instance_types {
         info!("Using instance type '{}'", instance_type);
 
+        let mut flex_subnet_ids = spec.clone().configuration.subnet_ids;
+
+        if flex_subnet_ids.len() <= 2 {
+            flex_subnet_ids.remove(0);
+        }
+
         // Run the ec2 instances
-        for subnet_id in &spec.configuration.subnet_ids {
+        for subnet_id in flex_subnet_ids {
             info!("Launching '{}' in '{}'", instance_type, subnet_id);
             memo.current_status = format!("Launching '{}' in '{}'", instance_type, subnet_id);
             client
@@ -247,7 +253,7 @@ where
                 .run_instances()
                 .min_count(instance_count)
                 .max_count(instance_count)
-                .subnet_id(subnet_id)
+                .subnet_id(subnet_id.clone())
                 .set_security_group_ids(if spec.configuration.security_groups.is_empty() {
                     None
                 } else {

bottlerocket/agents/src/bin/eks-resource-agent/eks_provider.rs

@@ -22,11 +22,12 @@ use serde_json::Value;
 use std::env::temp_dir;
 use std::path::Path;
 use std::process::Command;
+use std::str::FromStr;
 use testsys_model::{Configuration, SecretName};
 
 use std::fs::File;
 use std::io::Write;
-use strum_macros::EnumString;
+use strum_macros::{AsRefStr, EnumString};
 
 /// The default region for the cluster.
 const DEFAULT_REGION: &str = "us-west-2";
@@ -142,6 +143,17 @@ enum IPFamily {
     IPv4,
 }
 
+#[derive(Debug, EnumString, AsRefStr)]
+#[strum(serialize_all = "kebab-case")]
+enum AvailabilityZones {
+    #[strum(serialize = "us-west-2a")]
+    UsWest2a,
+    #[strum(serialize = "us-west-2b")]
+    UsWest2b,
+    #[strum(serialize = "us-west-2c")]
+    UsWest2c,
+}
+
 /// Configuration for setting up an EKS cluster using eksctl yaml file.
 ///
 /// # Fields:
@@ -239,10 +251,23 @@ struct ManagedNodeGroup {
     min_size: i32,
     /// The maximum number of nodes in the managed node group.
     max_size: i32,
-    // The desired number of nodes in the managed node group.
+    /// The desired number of nodes in the managed node group.
     desired_capacity: i32,
 }
 
+fn get_remaining_zones(exclude: String) -> Vec<AvailabilityZones> {
+    let all_zones = vec![
+        AvailabilityZones::UsWest2a,
+        AvailabilityZones::UsWest2b,
+        AvailabilityZones::UsWest2c,
+    ];
+
+    all_zones
+        .into_iter()
+        .filter(|zone| zone.as_ref() != exclude)
+        .collect()
+}
+
 #[allow(clippy::unwrap_or_default)]
 fn create_yaml(
     cluster_name: &str,
@@ -256,6 +281,24 @@ fn create_yaml(
         IPFamily::IPv4
     };
 
+    let mut eks_zones: Vec<String> = zones.clone().unwrap();
+
+    if zones.is_some() && zones.iter().len() < 2 {
+        let zones_upwrap = zones.clone().unwrap().first().unwrap().to_string();
+        if AvailabilityZones::from_str(&zones_upwrap).is_err() {
+            return Err(ProviderError::new_with_context(
+                Resources::Clear,
+                format!("Input zone of {} in Test.toml is invalid", zones_upwrap),
+            ));
+        }
+        let remain_zone = get_remaining_zones(zones_upwrap)
+            .first()
+            .unwrap()
+            .as_ref()
+            .to_string();
+        eks_zones.insert(0, remain_zone);
+    }
+
     let cluster = EksctlYamlConfig {
         api_version: "eksctl.io/v1alpha5".to_string(),
         kind: "ClusterConfig".to_string(),
@@ -264,7 +307,7 @@ fn create_yaml(
             region: region.to_string(),
             version: version.to_string(),
         },
-        availability_zones: zones.clone().unwrap_or_else(Vec::new),
+        availability_zones: eks_zones,
         kubernetes_network_config: KubernetesNetworkConfig {
             ip_family: set_ip_family,
         },