In order to connect to docker, you should firstly know the name of the docker container. This can be obtained as follows:

[root@tain-cx-uatdkrdb1 ~]# docker container ls
CONTAINER ID        IMAGE                                     COMMAND                  CREATED             STATUS              PORTS               NAMES
71e7c7016763        docker-registry.tain.com/cassandra:3.10   "/docker-entrypoint.…"   9 days ago          Up 9 days                               cas3
ea9b9f22c874        docker-registry.tain.com/cassandra:3.10   "/docker-entrypoint.…"   9 days ago          Up 9 days                               cas2
46fac822cffe        docker-registry.tain.com/cassandra:3.10   "/docker-entrypoint.…"   9 days ago          Up 9 days                               cas1

So in order to connect we can simply execute the /bin/bash on the container:

[root@tain-cx-uatdkrdb1 ~]# docker exec --help

Usage:  docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

Run a command in a running container

Options:
  -d, --detach               Detached mode: run command in the background
      --detach-keys string   Override the key sequence for detaching a container
  -e, --env list             Set environment variables
  -i, --interactive          Keep STDIN open even if not attached
      --privileged           Give extended privileges to the command
  -t, --tty                  Allocate a pseudo-TTY
  -u, --user string          Username or UID (format: <name|uid>[:<group|gid>])
  -w, --workdir string       Working directory inside the container
[root@tain-cx-uatdkrdb1 ~]# docker exec -it cas1 /bin/bash
root@46fac822cffe:/#    <- We are on 1st container :) 

Migration to and from the docker is done rather easily, even when you have to export a database or so:

The export from Mongo is done via the standard utils like: mongoexport, but firstly we have to see our container:

[root@tpb-mts-stdkr1 ~]# docker container ls
CONTAINER ID        IMAGE                                      COMMAND                  CREATED             STATUS              PORTS                                      NAMES
0ac74afee7b7        nginx:latest                               "nginx -g 'daemon of…"   7 weeks ago         Up 7 weeks          0.0.0.0:80->80/tcp, 0.0.0.0:443->443/tcp   production_nginx_1
c188736759e9        docker.tain.com/incident.backend:latest    "./server"               7 weeks ago         Up 33 hours         0.0.0.0:3000->8080/tcp                     production_incidenttool_backend_1
18e980dee75c        docker.tain.com/incident.frontend:latest   "nginx -g 'daemon of…"   7 weeks ago         Up 33 hours         0.0.0.0:8080->80/tcp                       production_incidenttool_frontend_1
8385665052a3        mongo                                      "docker-entrypoint.s…"   4 months ago        Up 33 hours         0.0.0.0:27017->27017/tcp                   production_incidenttool_mongo_1
e03d9bc636c5        mongo                                      "docker-entrypoint.s…"   5 months ago        Up 33 hours         0.0.0.0:27018->27017/tcp                   recordingtool_mongo_1
e4031dbf6b08        mongo-express                              "tini -- /docker-ent…"   5 months ago        Up 33 hours         0.0.0.0:8082->8081/tcp                     recordingtool_mongo_management_1
667870179b38        recordingtool/server:latest                "./server"               5 months ago        Up 33 hours                                                    recordingtool_server_1
5d37f142d32b        netdata/netdata                            "/usr/sbin/run.sh"       8 months ago        Up 27 hours         0.0.0.0:19999->19999/tcp                   netdata
(reverse-i-search)`': ^C

Then we can connect to it as follows:

[root@tpb-mts-stdkr1 ~]# docker exec -it 8385665052a3 /bin/bash

And then we can connect to the mongo, if we want to:

root@8385665052a3:/# mongo admin -u root -p password
MongoDB shell version v4.0.4
connecting to: mongodb://127.0.0.1:27017/admin
Implicit session: session { "id" : UUID("310e30d1-8cf6-4e4a-b1a4-206d3c9104a1") }
MongoDB server version: 4.0.4
Server has startup warnings:
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten]
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'.
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten]
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
2020-01-09T01:33:38.696+0000 I CONTROL  [initandlisten]
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Enable MongoDB's free cloud-based monitoring service, which will then receive and display
metrics about your deployment (disk utilization, CPU, operation statistics, etc).

The monitoring data will be available on a MongoDB website with a unique URL accessible to you
and anyone you share the URL with. MongoDB may use this information to make product
improvements and to suggest MongoDB products and deployment options to you.

To enable free monitoring, run the following command: db.enableFreeMonitoring()
To permanently disable this reminder, run the following command: db.disableFreeMonitoring()
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