@Override
  public void close() throws IOException {
    maybeUnsubscribeChangeTopic();
    open.set(false);
  }
Get an existing container from a given account.
@param accountId the name of account which container belongs to.
@param containerId the id of container to get.
@return the requested {@link Container} object or null if not present.
@throws AccountServiceException if exception occurs when getting container.
ambry-account/src/main/java/com/github/ambry/account/CachedAccountService.java