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Provide a way to implement a HealthChecker with periodic polling (#3406)
Motivation #3392 Let a server implement a HealthChecker that updates its healthiness by polling an external source (e.g. database) periodically. Modifications * Add factory method on HealthChecker interface to allow user to provide their asynchronous checking easily. * Implement `ScheduledHealthChecker` which can be used by multiple servers/HealthCheckService Result * Closes #3392
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core/src/main/java/com/linecorp/armeria/server/healthcheck/HealthCheckStatus.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,66 @@ | ||
| /* | ||
| * Copyright 2021 LINE Corporation | ||
| * | ||
| * LINE Corporation licenses this file to you under the Apache License, | ||
| * version 2.0 (the "License"); you may not use this file except in compliance | ||
| * with the License. You may obtain a copy of the License at: | ||
| * | ||
| * https://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT | ||
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the | ||
| * License for the specific language governing permissions and limitations | ||
| * under the Licenses | ||
| */ | ||
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| package com.linecorp.armeria.server.healthcheck; | ||
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| import static com.google.common.base.Preconditions.checkArgument; | ||
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| import com.google.common.base.MoreObjects; | ||
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| import com.linecorp.armeria.common.annotation.UnstableApi; | ||
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| /** | ||
| * The result of health check with interval for next check. | ||
| */ | ||
| @UnstableApi | ||
| public final class HealthCheckStatus { | ||
| private final boolean isHealthy; | ||
| private final long ttlMillis; | ||
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| /** | ||
| * Create the result of the health check. | ||
| * | ||
| * @param isHealthy health check result | ||
| * @param ttlMillis interval for scheduling the next check | ||
| */ | ||
| public HealthCheckStatus(boolean isHealthy, long ttlMillis) { | ||
| checkArgument(ttlMillis > 0, "ttlMillis: %s (expected: > 0)", ttlMillis); | ||
| this.isHealthy = isHealthy; | ||
| this.ttlMillis = ttlMillis; | ||
| } | ||
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| /** | ||
| * Return the result of health check. | ||
| */ | ||
| public boolean isHealthy() { | ||
| return isHealthy; | ||
| } | ||
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| /** | ||
| * Return the interval for scheduling the next check. | ||
| */ | ||
| public long ttlMillis() { | ||
| return ttlMillis; | ||
| } | ||
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| @Override | ||
| public String toString() { | ||
| return MoreObjects.toStringHelper(this) | ||
| .add("isHealthy", isHealthy) | ||
| .add("ttlMillis", ttlMillis) | ||
| .toString(); | ||
| } | ||
| } |
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core/src/main/java/com/linecorp/armeria/server/healthcheck/ScheduledHealthChecker.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,217 @@ | ||
| /* | ||
| * Copyright 2021 LINE Corporation | ||
| * | ||
| * LINE Corporation licenses this file to you under the Apache License, | ||
| * version 2.0 (the "License"); you may not use this file except in compliance | ||
| * with the License. You may obtain a copy of the License at: | ||
| * | ||
| * https://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT | ||
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the | ||
| * License for the specific language governing permissions and limitations | ||
| * under the Licenses | ||
| */ | ||
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| package com.linecorp.armeria.server.healthcheck; | ||
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| import java.time.Duration; | ||
| import java.util.concurrent.CompletionStage; | ||
| import java.util.concurrent.Future; | ||
| import java.util.concurrent.TimeUnit; | ||
| import java.util.concurrent.atomic.AtomicBoolean; | ||
| import java.util.concurrent.atomic.AtomicInteger; | ||
| import java.util.concurrent.atomic.AtomicReference; | ||
| import java.util.function.Consumer; | ||
| import java.util.function.Supplier; | ||
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| import org.slf4j.Logger; | ||
| import org.slf4j.LoggerFactory; | ||
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| import com.google.common.annotations.VisibleForTesting; | ||
| import com.google.common.util.concurrent.Futures; | ||
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| import com.linecorp.armeria.common.util.AbstractListenable; | ||
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| import io.netty.util.concurrent.EventExecutor; | ||
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| /** | ||
| * A {@link ListenableHealthChecker} whose state can be set by the result of supplied CompletionStage. | ||
| * This class can be shared by multiple {@link HealthCheckService}. | ||
| */ | ||
| final class ScheduledHealthChecker extends AbstractListenable<HealthChecker> | ||
| implements ListenableHealthChecker { | ||
| private final Supplier<? extends CompletionStage<HealthCheckStatus>> healthChecker; | ||
| private final Duration fallbackTtl; | ||
| private final EventExecutor eventExecutor; | ||
| private final Consumer<HealthChecker> onHealthCheckerUpdate; | ||
| private final AtomicBoolean isHealthy = new AtomicBoolean(); | ||
| private final AtomicInteger requestCount = new AtomicInteger(); | ||
| private final AtomicReference<ScheduledHealthCheckerImpl> impl = new AtomicReference<>(); | ||
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| ScheduledHealthChecker(Supplier<? extends CompletionStage<HealthCheckStatus>> healthChecker, | ||
| Duration fallbackTtl, EventExecutor eventExecutor) { | ||
| this.healthChecker = healthChecker; | ||
| this.fallbackTtl = fallbackTtl; | ||
| this.eventExecutor = eventExecutor; | ||
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| onHealthCheckerUpdate = latestValue -> { | ||
| isHealthy.set(latestValue.isHealthy()); | ||
| notifyListeners(latestValue); | ||
| }; | ||
| } | ||
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| @Override | ||
| public boolean isHealthy() { | ||
| return isHealthy.get(); | ||
| } | ||
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| void startHealthChecker() { | ||
| if (requestCount.getAndIncrement() != 0) { | ||
| return; | ||
| } | ||
| final ScheduledHealthCheckerImpl newlyScheduled = | ||
| new ScheduledHealthCheckerImpl(healthChecker, fallbackTtl, eventExecutor); | ||
| // This spin prevents the following race condition, which occurs when this instance is shared | ||
| // by more than one server instance: | ||
| // | ||
| // 1. Server A starts. | ||
| // 2. Server A stops. decrementAndGet() returns 0, but it didn't clear `impl` yet. | ||
| // 3. Server B starts; getAndIncrement() returns 0, but `impl` isn't `null` yet. | ||
| // | ||
| // There should be no unexpectedly long spin here, as long as a caller makes sure to call | ||
| // `stopHealthChecker()` for each `startHealthChecker()`, because this method is guarded by | ||
| // `requestCount.getAndIncrement()` to allow only the first request to start to schedule | ||
| // a task. | ||
| for (;;) { | ||
| if (impl.compareAndSet(null, newlyScheduled)) { | ||
| newlyScheduled.startHealthChecker(onHealthCheckerUpdate); | ||
| break; | ||
| } | ||
| } | ||
| } | ||
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| /** | ||
| * This method must be called after the paired startHealthChecker completes to | ||
| * guarantee the state consistency. | ||
| */ | ||
| void stopHealthChecker() { | ||
| final int currentCount = requestCount.decrementAndGet(); | ||
| // Must be called after startHealthChecker, so it's always greater than or equal to 0. | ||
| assert currentCount >= 0; | ||
| if (currentCount != 0) { | ||
| return; | ||
| } | ||
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| final ScheduledHealthCheckerImpl current = impl.getAndSet(null); | ||
| // Must be called after startHealthChecker, so it's always non null. | ||
| assert current != null; | ||
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| current.stopHealthChecker(onHealthCheckerUpdate); | ||
| } | ||
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| /** | ||
| * Used for test verification. | ||
| */ | ||
| @VisibleForTesting | ||
| int getRequestCount() { | ||
| return requestCount.get(); | ||
| } | ||
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| /** | ||
| * Used for test verification. | ||
| */ | ||
| @VisibleForTesting | ||
| boolean isActive() { | ||
| return impl.get() != null; | ||
| } | ||
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| /** | ||
| * Health checker can be scheduled only once. Calling startHealthChecker won't work after stopHealthChecker. | ||
| * This class itself is not thread-safe and guarded by {@link ScheduledHealthChecker} to avoid calling | ||
| * {@link ScheduledHealthChecker#startHealthChecker()} and | ||
| * {@link ScheduledHealthChecker#stopHealthChecker()} concurrently. | ||
| */ | ||
| private static final class ScheduledHealthCheckerImpl { | ||
| private static final Logger logger = LoggerFactory.getLogger(ScheduledHealthCheckerImpl.class); | ||
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| private final Supplier<? extends CompletionStage<HealthCheckStatus>> healthChecker; | ||
| private final Duration fallbackTtl; | ||
| private final EventExecutor eventExecutor; | ||
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| private final SettableHealthChecker settableHealthChecker = new SettableHealthChecker(false); | ||
| // The state will be set by startHealthChecker and stopHealthChecker, then read by another | ||
| // scheduled task in runHealthCheck. | ||
| private volatile State state = State.INIT; | ||
| private volatile Future<?> scheduledFuture = Futures.immediateVoidFuture(); | ||
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| ScheduledHealthCheckerImpl(Supplier<? extends CompletionStage<HealthCheckStatus>> healthChecker, | ||
| Duration fallbackTtl, EventExecutor eventExecutor) { | ||
| this.healthChecker = healthChecker; | ||
| this.fallbackTtl = fallbackTtl; | ||
| this.eventExecutor = eventExecutor; | ||
| } | ||
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| private void startHealthChecker(Consumer<? super HealthChecker> listener) { | ||
| if (state != State.INIT) { | ||
| return; | ||
| } | ||
| state = State.SCHEDULED; | ||
| settableHealthChecker.addListener(listener); | ||
| scheduledFuture = eventExecutor.submit(this::runHealthCheck); | ||
| } | ||
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| private void stopHealthChecker(Consumer<?> listener) { | ||
| if (state != State.SCHEDULED) { | ||
| return; | ||
| } | ||
| state = State.FINISHED; | ||
| scheduledFuture.cancel(true); | ||
| settableHealthChecker.removeListener(listener); | ||
| } | ||
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| private void runHealthCheck() { | ||
| if (state != State.SCHEDULED) { | ||
| return; | ||
| } | ||
| try { | ||
| healthChecker.get().handle((result, throwable) -> { | ||
| final boolean isHealthy; | ||
| final long intervalMillis; | ||
| if (throwable != null) { | ||
| logger.warn("Health checker throws an exception, schedule the next check after {}ms.", | ||
| fallbackTtl.toMillis(), throwable); | ||
| isHealthy = false; | ||
| intervalMillis = fallbackTtl.toMillis(); | ||
| } else if (result == null) { | ||
| logger.warn("Health checker returns an unexpected null result, " + | ||
| "schedule the next check after {}ms.", | ||
| fallbackTtl.toMillis()); | ||
| isHealthy = false; | ||
| intervalMillis = fallbackTtl.toMillis(); | ||
| } else { | ||
| isHealthy = result.isHealthy(); | ||
| intervalMillis = result.ttlMillis(); | ||
| } | ||
| settableHealthChecker.setHealthy(isHealthy); | ||
| scheduledFuture = eventExecutor.schedule(this::runHealthCheck, intervalMillis, | ||
| TimeUnit.MILLISECONDS); | ||
| return null; | ||
| }); | ||
| } catch (Throwable throwable) { | ||
| logger.warn("Health checker throws an exception, schedule the next check after {}ms.", | ||
| fallbackTtl.toMillis(), throwable); | ||
| settableHealthChecker.setHealthy(false); | ||
| scheduledFuture = eventExecutor.schedule(this::runHealthCheck, fallbackTtl.toMillis(), | ||
| TimeUnit.MILLISECONDS); | ||
| } | ||
| } | ||
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| enum State { | ||
| INIT, | ||
| SCHEDULED, | ||
| FINISHED | ||
| } | ||
| } | ||
| } |
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