# MongoDB Docker - Persist data

**URL:** <https://forums.suse.com/t/mongodb-docker-persist-data/5837>\
**Category:** General\
**Created:** [March 13, 2017, 6:19pm UTC](https://forums.suse.com/t/mongodb-docker-persist-data/5837 "2017-03-13T18:19:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![skofgar](https://sea2.discourse-cdn.com/flex022/user_avatar/forums.suse.com/skofgar/32/2249_2.png) [@skofgar](https://forums.suse.com/u/skofgar)\
**Post date:** [March 13, 2017, 6:19pm UTC](https://forums.suse.com/t/mongodb-docker-persist-data/5837/1 "2017-03-13T18:19:56Z")

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Hello everyone,  
I’m fairly new to Rancher, Cattle and Docker.  
I came across the blog entry on explaining how the[catalog entry for building a MongoDB was created](http://rancher.com/building-a-mongodb-catalog-item-for-rancher/). However, I do not entirely understand how the data of the MongoDB gets persisted. As far as I know Docker images are stateless. Now I noticed there are two sidekicks in that catalog entry: one for configuration/scripts and the second one for data storage.

So:

1. why does this work  
1.1 why can Docker store the data using another Docker image?
2. how it is useful to have that in a separate image?  
2.1. Is it, so that you can update the mongoDB image without loosing the data?
3. Is the data now _really_ stored or can it still get lost?
4. Sidekicks are a _Rancher & Cattle_ solution-right? I’ve never heard of them related to Docker before

Are there more documents about sidekicks available? I only found a [very short wiki article](http://docs.rancher.com/rancher/v1.5/en/cattle/adding-services/#sidekick-services).

Can you give me any pointers?

Have a great day!