display events in the CLI, document the use

bin/src/cli.rs

@@ -180,7 +180,7 @@ pub enum SubCmd {
         #[clap(subcommand)]
         cmd: ConfigCmd,
     },
-    #[clap(name = "events", about = "receive sozu events")]
+    #[clap(name = "events", about = "receive sozu events about the status of backends")]
     Events,
 }
 

bin/src/ctl/command.rs

@@ -46,6 +46,12 @@ impl CommandManager {
                     if !self.json {
                         debug!("Processing: {}", response.message);
                     }
+                    if let Some(ResponseContent {
+                        content_type: Some(ContentType::Event(event)),
+                    }) = response.content
+                    {
+                        info!("{}, {}", response.message, event);
+                    }
                 }
                 ResponseStatus::Failure => return Err(CtlError::Failure(response.message)),
                 ResponseStatus::Ok => return Ok(response),

command/src/command.proto

@@ -522,6 +522,7 @@ message ClusterInformation {
     repeated AddBackend backends = 5;
 }
 
+// an event produced by a worker to notify about backends status
 message Event {
     required EventKind kind = 1;
     optional string cluster_id = 2;

command/src/proto/display.rs

@@ -14,10 +14,11 @@ use crate::{
             filtered_metrics, protobuf_endpoint, request::RequestType,
             response_content::ContentType, AggregatedMetrics, AvailableMetrics, CertificateAndKey,
             CertificateSummary, CertificatesWithFingerprints, ClusterMetrics, CustomHttpAnswers,
-            FilteredMetrics, HttpEndpoint, HttpListenerConfig, HttpsListenerConfig,
-            ListOfCertificatesByAddress, ListedFrontends, ListenersList, ProtobufEndpoint,
-            QueryCertificatesFilters, RequestCounts, Response, ResponseContent, ResponseStatus,
-            RunState, SocketAddress, TlsVersion, WorkerInfos, WorkerMetrics, WorkerResponses,
+            Event, EventKind, FilteredMetrics, HttpEndpoint, HttpListenerConfig,
+            HttpsListenerConfig, ListOfCertificatesByAddress, ListedFrontends, ListenersList,
+            ProtobufEndpoint, QueryCertificatesFilters, RequestCounts, Response, ResponseContent,
+            ResponseStatus, RunState, SocketAddress, TlsVersion, WorkerInfos, WorkerMetrics,
+            WorkerResponses,
         },
         DisplayError,
     },
@@ -1006,3 +1007,26 @@ impl CustomHttpAnswers {
         rows
     }
 }
+
+impl Display for Event {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        let kind = match self.kind() {
+            EventKind::BackendDown => "backend down",
+            EventKind::BackendUp => "backend up",
+            EventKind::NoAvailableBackends => "no available backends",
+            EventKind::RemovedBackendHasNoConnections => "removed backend has no connections",
+        };
+        let address = match &self.address {
+            Some(a) => a.to_string(),
+            None => String::new(),
+        };
+        write!(
+            f,
+            "{}, backend={}, cluster={}, address={}",
+            kind,
+            self.backend_id(),
+            self.cluster_id(),
+            address,
+        )
+    }
+}

doc/configure_cli.md

@@ -94,3 +94,14 @@ sozu --config /etc/sozu/config.toml state load --file state.json
 ```
 
 You should be able to request your cluster like before the shutdown.
+
+### Monitor status of backends with events
+
+This CLI command:
+
+```bash
+sozu --config /path/to/config.toml events
+```
+
+listens to events sent by Sōzu workers whenever a backend is down, up again,
+or when no backend is available.