[GitHub] incubator-brooklyn pull request: Added basic migration capability ...

[sjcorbett <gi...@git.apache.org>]

Github user sjcorbett commented on a diff in the pull request:

    https://github.com/apache/incubator-brooklyn/pull/924#discussion_r46942466
  
    --- Diff: software/webapp/src/main/java/org/apache/brooklyn/entity/webapp/JavaWebAppMigrateEffector.java ---
    @@ -0,0 +1,115 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF 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
    + *
    + *     http://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 License.
    + */
    +package org.apache.brooklyn.entity.webapp;
    +
    +import com.google.common.collect.Lists;
    +import org.apache.brooklyn.api.entity.Entity;
    +import org.apache.brooklyn.api.entity.EntityInitializer;
    +import org.apache.brooklyn.api.entity.EntityLocal;
    +import org.apache.brooklyn.api.location.Location;
    +import org.apache.brooklyn.core.effector.EffectorBody;
    +import org.apache.brooklyn.core.entity.Entities;
    +import org.apache.brooklyn.core.entity.EntityInternal;
    +import org.apache.brooklyn.core.entity.lifecycle.Lifecycle;
    +import org.apache.brooklyn.core.entity.lifecycle.ServiceStateLogic;
    +import org.apache.brooklyn.core.entity.trait.Startable;
    +import org.apache.brooklyn.entity.software.base.AllowsMigration;
    +import org.apache.brooklyn.util.collections.MutableMap;
    +import org.apache.brooklyn.util.core.config.ConfigBag;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +public class JavaWebAppMigrateEffector implements EntityInitializer {
    +
    +    private static final Logger LOG = LoggerFactory.getLogger(JavaWebAppMigrateEffector.class);
    +
    +    @Override
    +    public void apply(final EntityLocal entity) {
    +        if (LOG.isDebugEnabled()) {
    +            LOG.debug("Adding Migrate effector to {}", entity);
    +        }
    +
    +        ((EntityInternal) entity).getMutableEntityType().addEffector(AllowsMigration.MIGRATE, new EffectorBody<Void>() {
    +            @Override
    +            public Void call(ConfigBag parameters) {
    +                migrate((EntityInternal) entity, (String) parameters.getStringKey(AllowsMigration.MIGRATE_LOCATION_SPEC));
    +                return null;
    +            }
    +        });
    +    }
    +
    +    private static void migrate(EntityInternal entity, String locationSpec) {
    +        if (ServiceStateLogic.getExpectedState(entity) != Lifecycle.RUNNING) {
    +            // Is it necessary to check if the whole application is healthy?
    +            throw new RuntimeException("The entity needs to be healthy before the migration starts");
    +        }
    +
    +        if (entity.getParent() != null && !entity.getParent().equals(entity.getApplication())) {
    +            /*
    +             * TODO: Allow nested entites to be migrated
    +             * If the entity has a parent different to the application root the migration cannot be done right now,
    +             * as it could lead into problems to deal with hierarchies like SameServerEntity -> Entity
    +             */
    +
    +            throw new RuntimeException("Nested entities cannot be migrated right now");
    +        }
    +
    +        // Retrieving the location from the catalog.
    +        Location newLocation = Entities.getManagementContext(entity).getLocationRegistry().resolve(locationSpec);
    +
    +        // TODO: Find a better way to check if you're migrating an entity to the exactly same VM. This not always works.
    +        for (Location oldLocation : entity.getLocations()) {
    +            if (oldLocation.containsLocation(newLocation)) {
    +                LOG.warn("You cannot migrate an entity to the same location, the migration process will stop right now");
    +                return;
    +            }
    +        }
    +
    +        LOG.info("Migration process of " + entity.getId() + " started.");
    +
    +        // When we have the new location, we free the resources of the current instance
    +        entity.invoke(Startable.STOP, MutableMap.<String, Object>of()).blockUntilEnded();
    +
    +        // Clearing old locations to remove the relationship with the previous instance
    +        entity.clearLocations();
    +        entity.addLocations(Lists.newArrayList(newLocation));
    +
    +        // Starting the new instance
    +        entity.invoke(Startable.START, MutableMap.<String, Object>of()).blockUntilEnded();
    +
    +        // Refresh all the dependent entities
    +
    +        for (Entity applicationChild : entity.getApplication().getChildren()) {
    +            // TODO: Find a better way to refresh the application configuration.
    +            // TODO: Refresh nested entities or find a way to propagate the restart properly.
    +
    +            // Restart any entity but the migrated one.
    +            if (applicationChild instanceof Startable) {
    +                if (entity.equals(applicationChild)) {
    +                    // The entity is sensors should rewired automatically on stop() + restart()
    +                } else {
    +                    // Restart the entity to fetch again all the dependencies (ie. attributeWhenReady ones)
    +                    ((Startable) applicationChild).restart();
    --- End diff --
    
    You're right that entities do not refresh themselves when sensors are republished. I didn't phrase it very well previously but I was trying to say that it is the job of the user of MigrateEffector to configure this. It's definitely possible if you create your application with Java. e.g. - 
    
    ```
    tomcat = EntitySpec.create(TomcatServer.class)
    nginx  = EntitySpec.create(NginxServer.class)
    nginx.subsribe(tomcat, sensor, sensorEventListenerThatUpdatesNginx'sConfig)
    ```
    I'm not sure if it's so straightforward from YAML. I'll take a look too.


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