I will share how to create an Private Docker Registry with Nexus3.x.
It built on Nexus, and provides GUI environment
I tried to write a lot of screenshots.

Demo Environment

Ubuntu 18.04
Docker version 18.09.1
- Docker requires at least > v1.8
Nexus 3.20.1

Install Nexus3 and create Private Docker Registry

Nexus ip is 182.252.133.70.

$ ssh root@182.252.133.70


#### 1) Create Host <-> Nexus container permanent volume
```bash
$ mkdir /nexus-data

2) Create Nexus container

$ docker run --name nexus -d -p 5000:5000 -p 8081:8081 -v /nexus-data:/nexus-data -u root sonatype/nexus3

3) Connect to Nexus web http://182.252.133.70:8081

First time, login admin account is required.
admin password find /nexus-data/admin.password

$ cat /nexus-data/admin.password
6f471aea-1d52-4e4b-9988-1714e9bf849d # admin's password

Enter a new admin password.

4) Create `docker-hosted` and `docker-proxy` Blob on Nexus

Gear > Repository > Blob Stores > Create blob store
You need to create docker-hosted and docker-hub.

Name : docker-hosted

Name : docker-hub

5) Create `docker-hosted` and `docker-proxy` Repository on Nexus

Gear > Repository > Repositories > Create repository
You need to create docker-hosted and docker-hub.

Select docker (hosted)

Name : docker-hosted
Check HTTP and input 5000
Check Enable Docker V1 API
Select Blob store docker-hosted

Select docker (proxy)

Name : docker-hub
Check Enable Docker V1 API
Input https://registry-1.docker.io in Remote storage
Select Use Docker Hub

6) Set Realms on Nexus

Gear > Realms > Move Docker Bearer Token Realm to active > Save

7) Set docker command http enabled (v1)

Create file /etc/docker/daemon.json
✔️ If the file does not exist, you must create it.

$ cat /etc/docker/daemon.json

{
        "insecure-registries" : ["182.252.133.70:5000"]
}

Restart docker daemon

$ service docker restart

Restart Nexus container

$ docker restart nexus

Push image from external client to Private Docker Registry

Client ip is 182.252.133.71.

$ ssh root@182.252.133.71


#### 1) Set docker command http enabled (v1)
Create file `/etc/docker/daemon.json` 
✔️ If the file does not exist, you must create it.
💥 All clients **must** be setting.

```bash
$ cat /etc/docker/daemon.json

{
        "insecure-registries" : ["182.252.133.70:5000"]
}

Restart docker daemon

$ service docker restart

2) Login Private Docker Registry

$ docker login 182.252.133.70:5000

Username: admin
Password:
WARNING! Your password will be stored unencrypted in /root/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded

3) docker pull and push Private Docker Registry

docker pull busybox image (from https://hub.docker.com/_/busybox)

$ docker pull busybox # docker pull from hub.docker.com 
bdbbaa22dec6: Pull complete
Digest: sha256:6915be4043561d64e0ab0f8f098dc2ac48e077fe23f488ac24b665166898115a
Status: Downloaded newer image for busybox:latest
docker.io/library/busybox:latest

Check busybox image

$ docker images -a
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
busybox             latest              6d5fcfe5ff17        5 weeks ago         1.22MB

tag

$ docker tag 6d5fcfe5ff17 182.252.133.70:5000/busybox:v20200205

push Private Docker Registry

$ docker push 182.252.133.70:5000/busybox:v20200205
The push refers to repository [182.252.133.70:5000/busybox]
195be5f8be1d: Pushed
v20200205: digest: sha256:edafc0a0fb057813850d1ba44014914ca02d671ae247107ca70c94db686e7de6 size: 527

Check image in Private Docker Registry

1) Connect to Nexus web http://182.252.133.70:8081

Browse > docker-hosted

tag

Pull in Private Docker Registry

$ docker pull 182.252.133.70:5000/busybox:v20200205
bdbbaa22dec6: Pull complete
Digest: sha256:edafc0a0fb057813850d1ba44014914ca02d671ae247107ca70c94db686e7de6
Status: Downloaded newer image for 182.252.133.70:5000/busybox:v20200205
182.252.133.70:5000/busybox:v20200205

$ docker images -a
REPOSITORY                    TAG                 IMAGE ID            CREATED             SIZE
182.252.133.70:5000/busybox   v20200205           6d5fcfe5ff17        5 weeks ago         1.22MB

More to do

443 port, need adding SSL

SSL should be applied.
After that, creating file /etc/docker/daemon.json can be omiited.
💡 I'll write this next posting.