Are there any well documented use cases of Apache ZooKeeper being used to distribute configuration of Java applications, and in particular Spring services?<\/p>\n
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>\n
UPDATE<\/strong><\/p>\n Eventually I ended up writing something that would load a ZooKeeper node as a properties file, and create a Are there any well documented use cases of Apache ZooKeeper being used to distribute configuration of Java applications, and in particular Spring services? 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. UPDATE Eventually […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4900","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4900","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=4900"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/4900\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=4900"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=4900"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=4900"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}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>\npublic class ZooKeeperPropertiesApplicationContextInitializer implements ApplicationContextInitializer {\n private static final Logger logger = LoggerFactory.getLogger(ZooKeeperPropertiesApplicationContextInitializer.class);\n\n private final CuratorFramework curator;\n private String projectName;\n private String projectVersion;\n\n public ZooKeeperPropertiesApplicationContextInitializer() throws IOException {\n logger.trace(\"Attempting to construct CuratorFramework instance\");\n\n RetryPolicy retryPolicy = new ExponentialBackoffRetry(10, 100);\n curator = CuratorFrameworkFactory.newClient(\"zookeeper\", retryPolicy);\n curator.start();\n }\n\n \/**\n * Add a primary property source to the application context, populated from\n * a pre-existing ZooKeeper node.\n *\/\n @Override\n public void initialize(ConfigurableApplicationContext applicationContext) {\n logger.trace(\"Attempting to add ZooKeeper-derived properties to ApplicationContext PropertySources\");\n\n try {\n populateProjectProperties();\n Properties properties = populatePropertiesFromZooKeeper();\n PropertiesPropertySource propertySource = new PropertiesPropertySource(\"zookeeper\", properties);\n applicationContext.getEnvironment().getPropertySources().addFirst(propertySource);\n\n logger.debug(\"Added ZooKeeper-derived properties to ApplicationContext PropertySources\");\n curator.close();\n } catch (IOException e) {\n logger.error(\"IO error attempting to load properties from ZooKeeper\", e);\n throw new IllegalStateException(\"Could not load ZooKeeper configuration\");\n } catch (Exception e) {\n logger.error(\"IO error attempting to load properties from ZooKeeper\", e);\n throw new IllegalStateException(\"Could not load ZooKeeper configuration\");\n } finally {\n if (curator != null && curator.isStarted()) {\n curator.close();\n }\n }\n }\n\n \/**\n * Populate the Maven artifact name and version from a property file that\n * should be on the classpath, with values entered via Maven filtering.\n * \n * There is a way of doing these with manifests, but it's a right faff when\n * creating shaded uber-jars.\n * \n * @throws IOException\n *\/\n private void populateProjectProperties() throws IOException {\n logger.trace(\"Attempting to get project name and version from properties file\");\n\n try {\n ResourcePropertySource projectProps = new ResourcePropertySource(\"project.properties\");\n this.projectName = (String) projectProps.getProperty(\"project.name\");\n this.projectVersion = (String) projectProps.getProperty(\"project.version\");\n } catch (IOException e) {\n logger.error(\"IO error trying to find project name and version, in order to get properties from ZooKeeper\");\n }\n }\n\n \/**\n * Do the actual loading of properties.\n * \n * @return\n * @throws Exception\n * @throws IOException\n *\/\n private Properties populatePropertiesFromZooKeeper() throws Exception, IOException {\n logger.debug(\"Attempting to get properties from ZooKeeper\");\n\n try {\n byte[] bytes = curator.getData().forPath(\"\/distributed-config\/\" + projectName + \"\/\" + projectVersion);\n InputStream in = new ByteArrayInputStream(bytes);\n Properties properties = new Properties();\n properties.load(in);\n return properties;\n } catch (NoNodeException e) {\n logger.error(\"Could not load application configuration from ZooKeeper as no node existed for project [{}]:[{}]\", projectName, projectVersion);\n throw e;\n }\n\n }\n\n}\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"