Added option to enable spot instance draining

Co-authored-by: Samuel Karp <samuelkarp@users.noreply.github.com>

README.md

@@ -389,6 +389,7 @@ These settings can be changed at any time.
   Bottlerocket sets this value to false by default. 
 * `settings.ecs.loglevel`: The level of verbosity for the ECS agent's logs.
   Supported values are `debug`, `info`, `warn`, `error`, and `crit`, and the default is `info`.
+* `settings.ecs.enable-spot-instance-draining`: If the instance receives a spot termination notice, the agent will set the instance's state to `DRAINING`, so the workload can be moved gracefully before the instance is removed. Defaults to `false`.
 
 #### Updates settings
 

sources/api/ecs-settings-applier/src/ecs.rs

@@ -45,6 +45,9 @@ struct ECSConfig {
 
     #[serde(rename = "OverrideAWSLogsExecutionRole")]
     override_awslogs_execution_role: bool,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    spot_instance_draining_enabled: Option<bool>,
 }
 
 // Returning a Result from main makes it print a Debug representation of the error, but with Snafu
@@ -90,6 +93,7 @@ fn run() -> Result<()> {
         // Always supported with Docker newer than v17.11.0
         // See https://github.com/docker/engine/commit/c7cc9d67590dd11343336c121e3629924a9894e9
         override_awslogs_execution_role: true,
+        spot_instance_draining_enabled: ecs.enable_spot_instance_draining,
         ..Default::default()
     };
     if let Some(os) = settings.os {

sources/api/migration/migrations/v1.0.1/add-enable-spot-instance-draining/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "add-enable-spot-instance-draining"
+version = "0.1.0"
+authors = ["Magnus Kulke <mkulke@gmail.com>"]
+license = "Apache-2.0 OR MIT"
+edition = "2018"
+publish = false
+# Don't rebuild crate just because of changes to README.
+exclude = ["README.md"]
+
+[dependencies]
+migration-helpers = { path = "../../../migration-helpers" }

sources/api/migration/migrations/v1.0.1/add-enable-spot-instance-draining/src/main.rs

@@ -0,0 +1,22 @@
+#![deny(rust_2018_idioms)]
+
+use migration_helpers::common_migrations::AddSettingsMigration;
+use migration_helpers::{migrate, Result};
+use std::process;
+
+/// We added a new setting, `ecs.enable-spot-instance-draining`
+fn run() -> Result<()> {
+    migrate(AddSettingsMigration(&[
+        "settings.ecs.enable-spot-instance-draining",
+    ]))
+}
+
+// Returning a Result from main makes it print a Debug representation of the error, but with Snafu
+// we have nice Display representations of the error, so we wrap "main" (run) and print any error.
+// https://github.com/shepmaster/snafu/issues/110
+fn main() {
+    if let Err(e) = run() {
+        eprintln!("{}", e);
+        process::exit(1);
+    }
+}

sources/models/src/lib.rs

@@ -113,6 +113,7 @@ struct ECSSettings {
     allow_privileged_containers: bool,
     logging_drivers: Vec<SingleLineString>,
     loglevel: ECSAgentLogLevel,
+    enable_spot_instance_draining: bool,
 }
 
 // Update settings. Taken from userdata. The 'seed' setting is generated