Port mappings are associated with containers

In addition to network access, docker provides two capabilities to meet the basic requirements of service access: one is to allow mapping of service ports applied within containers to local host hosts, and the other is to enable quick access through container names between multiple containers through an interconnection mechanism.

Port Mapping Container Access

1. Access container applications from outside. If you do not specify parameters when starting the container, network applications and services within the container cannot be accessed from outside the container through the network.Port mappings can be specified by the -P or -p parameters.
-P: Randomly map a port from 49000 to 49900 to a network port open to an internal container

[root@docker01 ~]# docker run -d -P training/webapp python app.py
75b2c32292d290aa3004b5b6cbb49775cc6f360796736473978cc32a682fdad9
[root@docker01 ~]# docker ps -l
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                     NAMES
75b2c32292d2        training/webapp     "python app.py"     3 seconds ago       Up 2 seconds        0.0.0.0:32770->5000/tcp   musing_carson

View application information

[root@docker01 ~]# docker logs -f musing_carson
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

2. Map all interface addresses, use HostPort:ContainerPort to map local port 5000 to container port 5000

[root@docker01 ~]# docker run -d -p 5000:5000 training/webapp python app.py
6368e0f567714ad90d2b20ff71afb2231e404b35639055a665cc3715a85f010a

Or use continuous-p binding to multiple ports

[root@docker01 ~]# docker run -d -p 5000:5000 -p3000:80 training/webapp python app.py
80bfe8e1f7fd53099e3f350c5efd1160a7247d065233965cc2bc2130e2fdcbb2

3. Map to the specified port at the specified address, using the IP:HostPort:ContainerPort format to specify that the mapping uses a specific address.

[root@docker01 ~]# docker run -d -p 10.10.17.199:5000:5000 training/webapp python app.py
ac228c0f2334a59856d9993e6a3eb652b50eb08ec41cedff87b331aa8d5d5f86
[root@docker01 ~]# docker ps -l
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                         NAMES
ac228c0f2334        training/webapp     "python app.py"     5 seconds ago       Up 5 seconds        10.10.17.199:5000->5000/tcp   eager_noether

4. Map to any port at the specified address, use IP::ContainerPort to bind any port of localhost to port 5000 of the container, and the local host will automatically assign a port

[root@docker01 ~]# docker run -d -p 127.0.0.1::5000 training/webapp python app.py
e72dec38ae77c113418156c4ad50b601fe31d0a38b4b8f995aabdcfcc510fdcc

Use UDP tags to specify UDP ports

[root@docker01 ~]# docker run -d -p 127.0.0.1:5001:5001/udp training/webapp python app.py
581ff1531c6b604c1b66ece82c87529a02c8da0b7b19e98bd336122c151b524f

5. View the mapped port configuration and use docker port to view the mapped port configuration

[root@docker01 ~]# docker port laughing_faraday 5000
127.0.0.1:32768

Interconnection mechanism for easy mutual access

Container interconnection is a quick way for applications in multiple containers to interact. It creates a connection relationship between the source and receive containers, which can be quickly accessed from the container name without specifying a specific IP address.
1. Customize the name of the container, and the connection system is based on the name of the container.First, you need a memorable container name. Although the system is not specified to assign one by default, the benefit of specifying one is that the name is memorable and is based on applications such as the web.When you need to connect other containers, you can also use the container name without changing it.

[root@docker01 ~]# docker run -d -P --name web training/webapp python app.py
6ae6d11614f99762a519d55beb8b38f3fbff667af34be90b33d6a11477b8d99a
[root@docker01 ~]# docker ps -l
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                     NAMES
6ae6d11614f9        training/webapp     "python app.py"     7 seconds ago       Up 6 seconds        0.0.0.0:32771->5000/tcp   web

2. Containers are interconnected, using the--link parameter allows safe interaction between containers
Create a new database container

[root@docker01 ~]# docker run -d --name db training/postgres
Unable to find image 'training/postgres:latest' locally
latest: Pulling from training/postgres
Image docker.io/training/postgres:latest uses outdated schema1 manifest format. Please upgrade to atibility. More information at https://docs.docker.com/registry/spec/deprecated-schema-v1/
a3ed95caeb02: Pull complete 
6e71c809542e: Pull complete 
2978d9af87ba: Pull complete 
e1bca35b062f: Pull complete 
500b6decf741: Pull complete 
74b14ef2151f: Pull complete 
7afd5ed3826e: Pull complete 
3c69bb244f5e: Pull complete 
d86f9ec5aedf: Pull complete 
010fabf20157: Pull complete 
Digest: sha256:a945dc6dcfbc8d009c3d972931608344b76c2870ce796da00a827bd50791907e
Status: Downloaded newer image for training/postgres:latest
67b752f9c5d6f19f2811674be780673b5475c845be6f43d9b15df139ff01c0fd

Delete the previous web container and create a new one to connect it to the db container

[root@docker01 ~]# docker rm -f web
web
[root@docker01 ~]# docker run -d -P --name web --link db:db training/webapp python app.py
de3f340d554dd01789859d6dc0fc3a0bb406e3111ca60e27f78da208def08dca

The--link parameter is formatted as--link name:alias, where name is the container name to link to and alias is the alias name.
Use docker ps to view links to containers

[root@docker01 ~]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                     NAMES
de3f340d554d        training/webapp     "python app.py"          4 minutes ago       Up 4 minutes        0.0.0.0:32772->5000/tcp   web
67b752f9c5d6        training/postgres   "su postgres -c '/us..."   13 minutes ago      Up 13 minutes       5432/tcp                  db

Equivalent to creating a virtual channel between two containers without mapping their ports to the host machine, starting the db container without using the -p or -P tag, avoiding exposing the database service end to the external network.
docker exposes connection information for containers in two ways
#Update environment variables
#Update/etc/hosts file
Use the env command to view the environment variables of the web container:

[root@docker01 ~]# docker run --rm --name web2 --link db:db training/webapp env
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=2ff63f7eb1d2
DB_PORT=tcp://172.17.0.3:5432
DB_PORT_5432_TCP=tcp://172.17.0.3:5432
DB_PORT_5432_TCP_ADDR=172.17.0.3
DB_PORT_5432_TCP_PORT=5432
DB_PORT_5432_TCP_PROTO=tcp
DB_NAME=/web2/db
DB_ENV_PG_VERSION=9.3
HOME=/root

In addition to the environment variable docker, host information is added to the parent container's/etc/hosts

[root@docker01 ~]# docker run -t -i --rm --link db:db training/webapp /bin/bash
root@8ed896541b8d:/opt/webapp# cat /etc/hosts
127.0.0.1   localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.3  db 67b752f9c5d6
172.17.0.4  8ed896541b8d
root@8ed896541b8d:/opt/webapp# ping db
PING db (172.17.0.3) 56(84) bytes of data.
64 bytes from db (172.17.0.3): icmp_seq=1 ttl=64 time=0.239 ms
64 bytes from db (172.17.0.3): icmp_seq=2 ttl=64 time=0.154 ms
64 bytes from db (172.17.0.3): icmp_seq=3 ttl=64 time=0.110 ms
64 bytes from db (172.17.0.3): icmp_seq=4 ttl=64 time=0.111 ms
^C
--- db ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3000ms
rtt min/avg/max/mdev = 0.110/0.153/0.239/0.053 ms

Users can link multiple child containers to the parent container, such as multiple web s to the same db container.