@Override
  public Container getContainerById(short accountId, Short containerId) throws AccountServiceException {
    return cachedAccountService.getContainerByIdHelper(accountId, containerId);
  }
Gets the {@link Container} by its Id and parent {@link Account} Id by looking up in in-memory cache.
If it is not present in in-memory cache, it queries from mysql db and updates the cache.
@param accountId the name of account which container belongs to.
@param containerId the id of container to get.
@return {@link Container} if found in cache or mysql db. Else, returns {@code null}.
@throws AccountServiceException
ambry-account/src/main/java/com/github/ambry/account/MySqlAccountService.java