Error in launcing app server in Heroku (and how to solve)

# Error in launcing app server in Heroku (And how to solve)
## Environments
* Heroku
* Memcachier
* Rails 5 API Mode
* MySQL ClearDB

## Error
```
2017-04-25T08:46:54.321621+00:00 app[web.1]: W, [2017-04-25T08:46:54.321561 #4]  WARN -- : localhost:11211 failed (count: 0) Errno::ECONNREFUSED: Connection refused - connect(2) for "localhost" port 11211
```

## source code (before resolve the problem)

### configuration file 

```config/environments/production.rb
  config.cache_store = :dalli_store,
    nil,
    { 
      :username => ENV["MEMCACHIER_USERNAME"],
      :password => ENV["MEMCACHIER_PASSWORD"],
      :failover => true,
      :socket_timeout => 1.5,
      :socket_failure_delay => 0.2,
      :down_retry_delay => 60,
      :expires_in => 7.day,
      :compress => true,
      :namespace => 'Planna-prod',
    }
```

note: According to [GitHub - petergoldstein/dalli: High performance memcached client for Ruby](https://github.com/petergoldstein/dalli)

> If your servers are specified in ENV["MEMCACHE_SERVERS"] (e.g. on Heroku when using a third-party hosted addon), simply provide nil for the servers:

Or simply  write configuration according to a Heroku document.

```config/environments/production.rb
  config.cache_store = :dalli_store,
    (ENV["MEMCACHIER_SERVERS"] || "").split(","),
    { 
      :username => ENV["MEMCACHIER_USERNAME"],
      :password => ENV["MEMCACHIER_PASSWORD"],
      :failover => true,
      :socket_timeout => 1.5,
      :socket_failure_delay => 0.2,
      :down_retry_delay => 60,
      :expires_in => 7.day,
      :compress => true,
      :namespace => 'Planna-prod',
```

and,  in  `config/application.rb` is a middleware configuration  as 

```
config.middleware.use ActionDispatch::Session::MemCacheStore, expires_after: 7.day
```

and, `config/initializers/session_store.rb` is

```
Rails.application.config.session_store :mem_cache_store
```

### environmental variables
Enviromental variables are set as below, 
* MEMCACHE_PASSWORD
* MEMCACHE_USERNAME
* MEMCACHE_SERVERS
* MEMCACHIER_PASSWORD
* MEMCACHIER_USERNAME
* MEMCACHIER_SERVERS

### the first try

Modify  `config/initializers/session_store.rb`  from

```
Rails.application.config.session_store :mem_cache_store
```

To 

```
Rails.application.config.session_store :dalli_store
```

### the second try
Modify `config/application.rb` from 

```
config.middleware.use ActionDispatch::Session::MemCacheStore, expires_after: 7.day
```

To 

```
require 'action_dispatch/middleware/session/dalli_store'
config.middleware.use ActionDispatch::Session::DalliStore, expires_after: 7.day
```

and then I encountered the same problem as  mentioned in this issue: https://github.com/petergoldstein/dalli/issues/613

so I tried to fix up the code the instruction In the issue 613.

> Update the value of config.cache_store in your environment configuration to be :dalli_store
> Set the config.session_store values to ActionDispatch::Session::CacheStore with whatever options you'd like

Then the problem in heroku  (the output is below)

```
2017-04-25T10:00:38.564394+00:00 heroku[web.1]: Process exited with status 0
2017-04-25T10:00:39.945440+00:00 heroku[web.1]: Starting process with command `bin/rails server -p 29870 -e production`
2017-04-25T10:00:42.430045+00:00 app[web.1]: /app/vendor/bundle/ruby/2.4.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:51: warning: constant ::Fixnum is deprecated
2017-04-25T10:00:42.430073+00:00 app[web.1]: /app/vendor/bundle/ruby/2.4.0/gems/activesupport-5.0.1/lib/active_support/xml_mini.rb:52: warning: constant ::Bignum is deprecated
2017-04-25T10:00:43.478293+00:00 app[web.1]: => Booting Puma
2017-04-25T10:00:43.478322+00:00 app[web.1]: => Rails 5.0.1 application starting in production on http://0.0.0.0:29870
2017-04-25T10:00:43.478323+00:00 app[web.1]: => Run `rails server -h` for more startup options
```