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POZooKeeper for Java/Spring Config?
 

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    <p>Are there any well documented use cases of Apache ZooKeeper being used to distribute configuration of Java applications, and in particular Spring services?</p> <p>Like many users of cloud services I have a requirement to change the configuration of a variable amount of Java services, preferably at run-time without needing to restart the services.</p> <p><strong>UPDATE</strong></p> <p>Eventually I ended up writing something that would load a ZooKeeper node as a properties file, and create a <code>ResourcePropertySource</code> and insert it into a Spring context. Note that this will not reflect changes in the ZooKeeper node after the context has started.</p> <pre><code>public class ZooKeeperPropertiesApplicationContextInitializer implements ApplicationContextInitializer&lt;ConfigurableApplicationContext&gt; { private static final Logger logger = LoggerFactory.getLogger(ZooKeeperPropertiesApplicationContextInitializer.class); private final CuratorFramework curator; private String projectName; private String projectVersion; public ZooKeeperPropertiesApplicationContextInitializer() throws IOException { logger.trace("Attempting to construct CuratorFramework instance"); RetryPolicy retryPolicy = new ExponentialBackoffRetry(10, 100); curator = CuratorFrameworkFactory.newClient("zookeeper", retryPolicy); curator.start(); } /** * Add a primary property source to the application context, populated from * a pre-existing ZooKeeper node. */ @Override public void initialize(ConfigurableApplicationContext applicationContext) { logger.trace("Attempting to add ZooKeeper-derived properties to ApplicationContext PropertySources"); try { populateProjectProperties(); Properties properties = populatePropertiesFromZooKeeper(); PropertiesPropertySource propertySource = new PropertiesPropertySource("zookeeper", properties); applicationContext.getEnvironment().getPropertySources().addFirst(propertySource); logger.debug("Added ZooKeeper-derived properties to ApplicationContext PropertySources"); curator.close(); } catch (IOException e) { logger.error("IO error attempting to load properties from ZooKeeper", e); throw new IllegalStateException("Could not load ZooKeeper configuration"); } catch (Exception e) { logger.error("IO error attempting to load properties from ZooKeeper", e); throw new IllegalStateException("Could not load ZooKeeper configuration"); } finally { if (curator != null &amp;&amp; curator.isStarted()) { curator.close(); } } } /** * Populate the Maven artifact name and version from a property file that * should be on the classpath, with values entered via Maven filtering. * * There is a way of doing these with manifests, but it's a right faff when * creating shaded uber-jars. * * @throws IOException */ private void populateProjectProperties() throws IOException { logger.trace("Attempting to get project name and version from properties file"); try { ResourcePropertySource projectProps = new ResourcePropertySource("project.properties"); this.projectName = (String) projectProps.getProperty("project.name"); this.projectVersion = (String) projectProps.getProperty("project.version"); } catch (IOException e) { logger.error("IO error trying to find project name and version, in order to get properties from ZooKeeper"); } } /** * Do the actual loading of properties. * * @return * @throws Exception * @throws IOException */ private Properties populatePropertiesFromZooKeeper() throws Exception, IOException { logger.debug("Attempting to get properties from ZooKeeper"); try { byte[] bytes = curator.getData().forPath("/distributed-config/" + projectName + "/" + projectVersion); InputStream in = new ByteArrayInputStream(bytes); Properties properties = new Properties(); properties.load(in); return properties; } catch (NoNodeException e) { logger.error("Could not load application configuration from ZooKeeper as no node existed for project [{}]:[{}]", projectName, projectVersion); throw e; } } } </code></pre>
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    1. COWhat kind of config changes do you want to push? Basic stuff like strings/ints/booleans? Or object wiring/DI changes?
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    2. COTo be frank, the most common change would be logging levels, although system admins have expressed an interest in things liek connection URLs for data stores.
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    3. COCould you please provide your `ResourcePropertySource` and `context.xml` examples? Or do you use `ConfigurableApplicationContext`? I can't get context started because of properties absence. Thanks in advance!
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      1. USAnton Kirillov
 

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