Clojure 微服务架构实战：服务发现、网关与观测

;; 每个服务暴露 /healthz，供探针与注册中心轮询
(defn health-handler [_]
  {:status 200 :body (json/write-str {:status "ok" :ts (System/currentTimeMillis)})})

;; 组合 Liveness（存活）与 Readiness（就绪）
(defn liveness [_] {:status 200 :body "alive"})
(defn readiness [deps]
  (fn [_]
    (if (db/ping (:db deps)) {:status 200} {:status 503})))

;; 网关：解析 JWT → 路由转发 → 聚合
(defn auth-middleware [handler]
  (fn [req]
    (if-let [claims (jwt/verify (:token req))]
      (handler (assoc req :claims claims))
      {:status 401 :body "unauthorized"})))

(def gateway-app
  (-> (reitit/router
        [["/api/orders/**" {:middleware [auth-middleware] :get (fn [req] (forward-to "order-svc" req))}]
         ["/api/users/**"  {:middleware [auth-middleware] :get (fn [req] (forward-to "user-svc" req))}]])
      (reitit/ring-handler)))

;; 集中读取配置：环境变量覆盖默认值
(def config
  (memoize
    (fn []
      {:db-host (or (System/getenv "DB_HOST") "localhost")
       :db-port (or (System/getenv "DB_PORT") "5432")
       :redis   (or (System/getenv "REDIS_URL") "redis://localhost")
       :mq      (or (System/getenv "MQ_URL") "kafka://localhost:9092")})))

(defn get-config [] (config))

;; 结构化日志（JSON），便于集中采集
(require '[jsonista.core :as json])

(defn log [level event ctx]
  (println (json/write-value-as-string
             {:level level :event event :ts (System/currentTimeMillis)
              :service (:service env) :ctx ctx})))

(require '[prometheus.clj :as prom])

(def orders-counter (prom/counter :orders_total "累计订单数"))
(def latency-hist   (prom/histogram :order_latency_seconds "订单耗时"))

(defn record-order! []
  (prom/inc orders-counter)
  (prom/time! latency-hist (do (place-order!) ...)))

;; 注入/透传 trace context，跨服务串联
(defn with-trace [ctx f]
  (let [span (ot/inject ctx)]
    (try (f) (finally (ot/finish span)))))

;; deps.edn + tools.build 打 uberjar
(defn build-uber [_]
  (uberjar {:basis (clojure/create-basis {})
           :main 'my.service.core}))

;; 极小镜像（配合 GraalVM native-image 可到几十 MB）
FROM gcr.io/distroless/java17-debian11:nonroot
COPY target/app.jar /app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

apiVersion: apps/v1
kind: Deployment
metadata: { name: order-svc }
spec:
  replicas: 3
  selector: { matchLabels: { app: order-svc } }
  template:
    metadata: { labels: { app: order-svc } }
    spec:
      containers:
        - name: app
          image: registry/order-svc:1.2.0
          ports: [{ containerPort: 8080 }]
          readinessProbe:
            httpGet: { path: /readyz, port: 8080 }
          livenessProbe:
            httpGet: { path: /livez, port: 8080 }
          envFrom: [{ secretRef: { name: app-secrets } }]
---
apiVersion: v1
kind: Service
metadata: { name: order-svc }
spec:
  selector: { matchLabels: { app: order-svc } }
  ports: [{ port: 80, targetPort: 8080 }]

;; 订单 Saga：下单 → 扣库存 → 支付，任一失败走补偿
(def steps
  [{:name :create-order :do create-order! :compensate cancel-order!}
   {:name :reserve-stock :do reserve-stock! :compensate release-stock!}
   {:name :charge        :do charge!        :compensate refund!}])

(defn run-saga [steps ctx]
  (loop [steps steps, ctx ctx, done []]
    (if-let [step (first steps)]
      (let [res (try {:ok ((:do step) ctx)} (catch Exception e {:err e}))]
        (if (:ok res)
          (recur (rest steps) (:ok res) (conj done step))
          ;; 失败 → 逆序补偿
          (doseq [s (reverse done)] ((:compensate s) ctx))
          res))
      {:ok ctx})))