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Last pushed: 14 days ago
Short Description
a Docker Networking Trouble-shooting Swiss-Army Container
Full Description

netshoot: a Docker network trouble-shooting swiss-army container

Purpose: Docker network tshooting can be difficult for network engineers. With proper understanding of how Docker networking works and the right set of tools, you can troubleshoot and resolve these networking issues. The netshoot container has a set of powerful networking tshooting tools that can be used to troubleshoot Docker networking issues.

Network Namespaces: Before starting to use this tool, it's important to go over one key topic: Network Namespaces. Network namespaces provide isolation of the system resources associated with networking. Docker uses network and other type of namespaces (pid,mount,user..etc) to create an isolated environment for each container. Everything from interfaces, routes, and IPs is completely isolated within the network namespace of the container.

Cool thing about namespaces is that you can switch between them. You can enter a different container's network namespace, perform some troubleshooting on its network's stack with tools that aren't even installed on that container. Additionally, netshoot can be used to troubleshoot the host itself by using the host's network namespace. This allows you to perform any troubleshooting without installing any new packages directly on the host or your application's package.

  • Container's Network Namespace: If you're having networking issues with your application's container, you can launch netshoot with that container's network namespace like this :

$ docker run -it --net container:<container_name> nicolaka/netshoot

  • Host's Network Namespace: If you think the networking issue is on the host itself, you can launch netshoot with that host's network namespace. This is how:

$ docker run -it --net host nicolaka/netshoot

  • Network's Network Namespace: If you want to troubleshoot a Docker network, you can enter the network's namespace using nsenter. This is explained in the nsenter section below.

Network Problems: Many network issues could result in application performance degradations. Some of those issues could be related to the underlying networking infrastructure(underlay). Others could be related to misconfiguration at the host or Docker level. Let's take a look at common networking issues:

  • latency
  • routing
  • DNS resolution
  • firewall
  • incomplete ARPs

To troubleshoot these issues, netshoot includes a set of powerful tools as recommended by this diagram.

Included Packages: The following packages are included in netshoot. We'll go over some with some sample use-cases.

  • iperf
  • tcpdump
  • netstat
  • iftop
  • drill
  • netcat-openbsd
  • iproute2
  • util-linux(nsenter)
  • bridge-utils
  • iputils
  • curl
  • ethtool
  • nmap
  • ipvs
  • ngrep

iperf

Purpose : test networking performance between two containers/hosts.

Create Overlay network:

$docker network create -d overlay perf-test

Launch two containers:

šŸ³  ā†’ docker service create --name perf-test-a --network perf-test nicolaka/netshoot iperf -s -p 9999
7dkcckjs0g7b4eddv8e5ez9nv


šŸ³  ā†’ docker service create --name perf-test-b --network perf-test nicolaka/netshoot iperf -c perf-test-a -p 9999
2yb6fxls5ezfnav2z93lua8xl



 šŸ³  ā†’ docker service ls
ID            NAME         REPLICAS  IMAGE              COMMAND
2yb6fxls5ezf  perf-test-b  1/1       nicolaka/netshoot  iperf -c perf-test-a -p 9999
7dkcckjs0g7b  perf-test-a  1/1       nicolaka/netshoot  iperf -s -p 9999



šŸ³  ā†’ docker ps
CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS              PORTS               NAMES
ce4ff40a5456        nicolaka/netshoot:latest   "iperf -s -p 9999"       31 seconds ago      Up 30 seconds                           perf-test-a.1.bil2mo8inj3r9nyrss1g15qav

šŸ³  ā†’ docker logs ce4ff40a5456
------------------------------------------------------------
Server listening on TCP port 9999
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 10.0.3.3 port 9999 connected with 10.0.3.5 port 35102
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  32.7 GBytes  28.1 Gbits/sec
[  5] local 10.0.3.3 port 9999 connected with 10.0.3.5 port 35112

tcpdump

tcpdump is a powerful and common packet analyzer that runs under the command line. It allows the user to display TCP/IP and other packets being transmitted or received over an attached network interface.

# Continuing on the iperf example. Let's lauch netshoot with perf-test-a's container network namespace.

šŸ³  ā†’ docker run -it --net container:perf-test-a.1.0qlf1kaka0cq38gojf7wcatoa  nicolaka/netshoot 

# Capturing packets on eth0 and tcp port 9999.

/ # tcpdump -i eth0 port 9999 -c 1 -Xvv
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
23:14:09.771825 IP (tos 0x0, ttl 64, id 60898, offset 0, flags [DF], proto TCP (6), length 64360)
    10.0.3.5.60032 > 0e2ccbf3d608.9999: Flags [.], cksum 0x1563 (incorrect -> 0x895d), seq 222376702:222441010, ack 3545090958, win 221, options [nop,nop,TS val 2488870 ecr 2488869], length 64308
    0x0000:  4500 fb68 ede2 4000 4006 37a5 0a00 0305  E..h..@.@.7.....
    0x0010:  0a00 0303 ea80 270f 0d41 32fe d34d cb8e  ......'..A2..M..
    0x0020:  8010 00dd 1563 0000 0101 080a 0025 fa26  .....c.......%.&
    0x0030:  0025 fa25 0000 0000 0000 0001 0000 270f  .%.%..........'.
    0x0040:  0000 0000 0000 0000 ffff d8f0 3435 3637  ............4567
    0x0050:  3839 3031 3233 3435 3637 3839 3031 3233  8901234567890123
    0x0060:  3435 3637 3839 3031 3233 3435 3637 3839  4567890123456789
    0x0070:  3031 3233 3435 3637 3839 3031 3233 3435  0123456789012345
    0x0080:  3637 3839 3031 3233 3435 3637 3839 3031  6789012345678901
    0x0090:  3233 3435 3637 3839 3031 3233 3435 3637  2345678901234567
    0x00a0:  3839 3031 3233 3435 3637 3839 3031 3233  8901234567890123
    0x00b0:  3435 3637 3839 3031 3233 3435 3637 3839  4567890123456789
    0x00c0:  3031 3233 3435 3637 3839 3031 3233 3435  0123456789012345
    0x00d0:  3637 3839 3031 3233 3435 3637 3839 3031  6789012345678901
    0x00e0:  3233 3435 3637 3839 3031 3233 3435 3637  2345678901234567
    0x00f0:  3839 3031 3233 3435 3637 3839 3031 3233  8901234567890123
    0x0100:  3435 3637 3839 3031 3233 3435 3637 3839  4567890123456789

More info on tcpdump can be found here.

netstat

Purpose: netstat is a useful tool for checking your network configuration and activity.

Continuing on from iperf example. Let's use netstat to confirm that it's listening on port 9999.

šŸ³  ā†’ docker run -it --net container:perf-test-a.1.0qlf1kaka0cq38gojf7wcatoa  nicolaka/netshoot 

/ # netstat -tulpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.11:46727        0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:9999            0.0.0.0:*               LISTEN      -
udp        0      0 127.0.0.11:39552        0.0.0.0:*                           -

nmap

nmap ("Network Mapper") is an open source tool for network exploration and security auditing. It is very useful for scanning to see which ports are open between a given set of hosts. This is a common thing to check for when installing Swarm or UCP because a range of ports is required for cluster communication. The command analyzes the connection pathway between the host where nmap is running and the given target address.

šŸ³  ā†’ docker run -it --privileged nicolaka/netshoot nmap -p 12376-12390 -dd 172.31.24.25

...
Discovered closed port 12388/tcp on 172.31.24.25
Discovered closed port 12379/tcp on 172.31.24.25
Discovered closed port 12389/tcp on 172.31.24.25
Discovered closed port 12376/tcp on 172.31.24.25
...

There are several states that ports will be discovered as:

  • open: the pathway to the port is open and there is an application listening on this port.
  • closed: the pathway to the port is open but there is no application listening on this port.
  • filtered: the pathway to the port is closed, blocked by a firewall, routing rules, or host-based rules.

iftop

Purpose: iftop does for network usage what top does for CPU usage. It listens to network traffic on a named interface and displays a table of current bandwidth usage by pairs of hosts.

Continuing the iperf example.

 ā†’ docker ps
CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS              PORTS               NAMES
ce4ff40a5456        nicolaka/netshoot:latest   "iperf -s -p 9999"       5 minutes ago       Up 5 minutes                            perf-test-a.1.bil2mo8inj3r9nyrss1g15qav

šŸ³  ā†’ docker run -it --net container:perf-test-a.1.bil2mo8inj3r9nyrss1g15qav nicolaka/netshoot iftop -i eth0

drill

Purpose: drill is a tool to designed to get all sorts of information out of the DNS.

Continuing the iperf example, we'll use drill to understand how services' DNS is resolved in Docker.

šŸ³  ā†’ docker run -it --net container:perf-test-a.1.bil2mo8inj3r9nyrss1g15qav nicolaka/netshoot drill -V 5 perf-test-b
;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 0
;; flags: rd ; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;; perf-test-b.    IN    A

;; ANSWER SECTION:

;; AUTHORITY SECTION:

;; ADDITIONAL SECTION:

;; Query time: 0 msec
;; WHEN: Thu Aug 18 02:08:47 2016
;; MSG SIZE  rcvd: 0
;; ->>HEADER<<- opcode: QUERY, rcode: NOERROR, id: 52723
;; flags: qr rd ra ; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;; perf-test-b.    IN    A

;; ANSWER SECTION:
perf-test-b.    600    IN    A    10.0.3.4 <<<<<<<<<<<<<<<<<<<<<<<<<< Service VIP

;; AUTHORITY SECTION:

;; ADDITIONAL SECTION:

;; Query time: 1 msec
;; SERVER: 127.0.0.11 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Local resolver 
;; WHEN: Thu Aug 18 02:08:47 2016
;; MSG SIZE  rcvd: 56

netcat

Purpose: a simple Unix utility that reads and writes data across network connections, using the TCP or UDP protocol. It's useful for testing and troubleshooting TCP/UDP connections. If there's a firewall rule blocking certain ports, netcat can be used to detect

šŸ³  ā†’  docker network create -d overlay my-ovl
55rohpeerwqx8og4n0byr0ehu

šŸ³  ā†’ docker service create --name service-a --network my-ovl -p 8080:8080 nicolaka/netshoot nc -l 8080
bnj517hh4ylpf7ewawsp9unrc

šŸ³  ā†’ docker service create --name service-b --network my-ovl nicolaka/netshoot nc -vz service-a 8080
3xv1ukbd3kr03j4uybmmlp27j

šŸ³  ā†’ docker logs service-b.1.0c5wy4104aosovtl1z9oixiso
Connection to service-a 8080 port [tcp/http-alt] succeeded!

netgen

netgen is a simple script that will generate a packet of data between containers periodically using netcat. It's purpose is to use the generated traffic to demonstrate different features of the networking stack.

netgen <host> <ip> will create a netcat server and client listening and sending to the same port.

Using netgen with docker run:

šŸ³  ā†’  docker network create -d bridge br
01b167971453700cf0a40d7e1a0dc2b0021e024bbb119541cc8c1858343c9cfc

šŸ³  ā†’  docker run -d --rm --net br --name c1 nicolaka/netshoot netgen c2 5000
8c51eb2100c35d14244dcecb80839c780999159985415a684258c7154ec6bd42

šŸ³  ā†’  docker run -it --rm --net br --name c2 nicolaka/netshoot netgen c1 5000
Listener started on port 5000
Sending traffic to c1 on port 5000 every 10 seconds
Sent 1 messages to c1:5000
Sent 2 messages to c1:5000

šŸ³  ā†’  sudo tcpdump -vvvn -i eth0 port 5000
...

Using netgen with docker services:

šŸ³  ā†’  docker network create -d overlay ov
01b167971453700cf0a40d7e1a0dc2b0021e024bbb119541cc8c1858343c9cfc

šŸ³  ā†’  docker service create --network ov --replicas 3 --name srvc netshoot netgen srvc 5000
y93t8mb9wgzsc27f7l2rdu5io

šŸ³  ā†’  docker service logs srvc
srvc.1.vwklts5ybq5w@moby    | Listener started on port 5000
srvc.1.vwklts5ybq5w@moby    | Sending traffic to srvc on port 5000 every 10 seconds
srvc.1.vwklts5ybq5w@moby    | Sent 1 messages to srvc:5000
srvc.3.dv4er00inlxo@moby    | Listener started on port 5000
srvc.2.vu47gf0sdmje@moby    | Listener started on port 5000
...


šŸ³  ā†’  sudo tcpdump -vvvn -i eth0 port 5000
...

iproute2

purpose: a collection of utilities for controlling TCP / IP networking and traffic control in Linux.

# Sample routing and arp table of the docker host.

šŸ³  ā†’ docker run -it --net host nicolaka/netshoot

/ # ip route show
default via 192.168.65.1 dev eth0  metric 204
172.17.0.0/16 dev docker0  proto kernel  scope link  src 172.17.0.1
172.19.0.0/16 dev br-fd694678f5c3  proto kernel  scope link  src 172.19.0.1 linkdown
172.20.0.0/16 dev docker_gwbridge  proto kernel  scope link  src 172.20.0.1
172.21.0.0/16 dev br-0d73cc4ac114  proto kernel  scope link  src 172.21.0.1 linkdown
172.22.0.0/16 dev br-1eb1f1e84df8  proto kernel  scope link  src 172.22.0.1 linkdown
172.23.0.0/16 dev br-aafed4ec941f  proto kernel  scope link  src 172.23.0.1 linkdown
192.168.65.0/29 dev eth0  proto kernel  scope link  src 192.168.65.2

/ # ip neigh show
192.168.65.1 dev eth0 lladdr f6:16:36:bc:f9:c6 STALE
172.17.0.7 dev docker0 lladdr 02:42:ac:11:00:07 STALE
172.17.0.6 dev docker0 lladdr 02:42:ac:11:00:06 STALE
172.17.0.5 dev docker0 lladdr 02:42:ac:11:00:05 STALE

More info on iproute2 here

nsenter

Prupose: nsenter is a powerful tool allowing you to enter into any namespaces. nsenter is available inside netshoot but requires netshoot to be run as a privileged container. Additionally, you may want to mount the /var/run/docker/netns directory to be able to enter any network namespace including bridge and overlay networks.

With docker run --name container-B --net container:container-A, docker uses container-A's network namespace ( including interfaces and routes) when creating container-B. This approach is helpful for troubleshooting network issues at the container level. To troubleshoot network issues at the bridge or overlay network level, you need to enter the namespace of the network itself. nsenter allows you to do that.

For example, if we wanted to check the L2 forwarding table for a overlay network. We need to enter the overlay network namespace and use same tools in netshoot to check these entries. The following examples go over some use cases for using nsenter to understand what's happening within a docker network ( overlay in this case).

# Creating an overlay network
šŸ³  ā†’ docker network create -d overlay nsenter-test
9tp0f348donsdj75pktssd97b

# Launching a simple busybox service with 3 replicas
šŸ³  ā†’ docker service create --name nsenter-l2-table-test --replicas 3 --network nsenter-test busybox ping localhost
3692i3q3u8nephdco2c10ro4c

# Inspecting the service
šŸ³  ā†’ docker network inspect nsenter-test
[
    {
        "Name": "nsenter-test",
        "Id": "9tp0f348donsdj75pktssd97b",
        "Scope": "swarm",
        "Driver": "overlay",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "10.0.1.0/24",
                    "Gateway": "10.0.1.1"
                }
            ]
        },
        "Internal": false,
        "Containers": {
            "0ebe0fab555d2e2ef2fcda634bef2071ad3f5842b06bd134b40f259ab9be4f13": {
                "Name": "nsenter-l2-table-test.2.83uezc16jcaz2rp6cjwyf4605",
                "EndpointID": "3064946bb0224a4b3647cefcba18dcbea71b90a2ba1c09212a7bc599ec1ed3eb",
                "MacAddress": "02:42:0a:00:01:04",
                "IPv4Address": "10.0.1.4/24",
                "IPv6Address": ""
            },
            "55065360ac1c71638fdef50a073a661dec53b693409c5e09f8f854abc7dbb373": {
                "Name": "nsenter-l2-table-test.1.4ryh3wmmv21nsrfwmilanypqq",
                "EndpointID": "f81ae5f979d6c54f60636ca9bb2107d95ebf9a08f64786c549e87a66190f1b1f",
                "MacAddress": "02:42:0a:00:01:03",
                "IPv4Address": "10.0.1.3/24",
                "IPv6Address": ""
            },
            "57eca277749bb01a488f0e6c4e91dc6720b7c8f08531536377b29a972971f54b": {
                "Name": "nsenter-l2-table-test.3.9cuoq5m2ue1wi4lsw64k88tvz",
                "EndpointID": "ff1a251ffd6c674cd5fd117386d1a197ab68b4ed708187035d91ff5bd5fe0251",
                "MacAddress": "02:42:0a:00:01:05",
                "IPv4Address": "10.0.1.5/24",
                "IPv6Address": ""
            }
        },
        "Options": {
            "com.docker.network.driver.overlay.vxlanid_list": "260"
        },
        "Labels": {}
    }
]

# Launcing netshoot in privileged mode
 šŸ³  ā†’ docker run -it --rm -v /var/run/docker/netns:/var/run/docker/netns --privileged=true nicolaka/netshoot

# Listing all docker-created network namespaces

 / # cd /var/run/docker/netns/
/var/run/docker/netns # ls
0b1b36d33313  1-9tp0f348do  14d1428c3962  645eb414b538  816b96054426  916dbaa7ea76  db9fd2d68a9b  e79049ce9994  f857b5c01ced
1-9r17dodsxt  1159c401b8d8  1a508036acc8  7ca29d89293c  83b743f2f087  aeed676a57a5  default       f22ffa5115a0


# The overlay network that we created had an id of 9tp0f348donsdj75pktssd97b. All overlay networks are named <number>-<id>. We can see it in the list as `1-9tp0f348do`. To enter it:

/ # nsenter --net=/var/run/docker/netns/1-9tp0f348do sh

# Now all the commands we issue are within that namespace. 

/ # ifconfig
br0       Link encap:Ethernet  HWaddr 02:15:B8:E7:DE:B3
          inet addr:10.0.1.1  Bcast:0.0.0.0  Mask:255.255.255.0
          inet6 addr: fe80::20ce:a5ff:fe63:437d%32621/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1
          RX packets:36 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2224 (2.1 KiB)  TX bytes:1348 (1.3 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1%32621/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1
          RX bytes:336 (336.0 B)  TX bytes:336 (336.0 B)

veth2     Link encap:Ethernet  HWaddr 02:15:B8:E7:DE:B3
          inet6 addr: fe80::15:b8ff:fee7:deb3%32621/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1
          RX packets:9 errors:0 dropped:0 overruns:0 frame:0
          TX packets:32 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:690 (690.0 B)  TX bytes:2460 (2.4 KiB)

veth3     Link encap:Ethernet  HWaddr 7E:55:C3:5C:C2:78
          inet6 addr: fe80::7c55:c3ff:fe5c:c278%32621/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1
          RX packets:13 errors:0 dropped:0 overruns:0 frame:0
          TX packets:26 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:970 (970.0 B)  TX bytes:1940 (1.8 KiB)

veth4     Link encap:Ethernet  HWaddr 72:95:AB:A1:6A:87
          inet6 addr: fe80::7095:abff:fea1:6a87%32621/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1
          RX packets:14 errors:0 dropped:0 overruns:0 frame:0
          TX packets:27 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1068 (1.0 KiB)  TX bytes:2038 (1.9 KiB)

vxlan1    Link encap:Ethernet  HWaddr EA:EC:1D:B1:7D:D7
          inet6 addr: fe80::e8ec:1dff:feb1:7dd7%32621/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1450  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:33 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

# Let's check out the L2 forwarding table. These MAC addresses belong to the tasks/containers in this service. 

/ # bridge  fdb show br br0
33:33:00:00:00:01 dev br0 self permanent
01:00:5e:00:00:01 dev br0 self permanent
33:33:ff:63:43:7d dev br0 self permanent
ea:ec:1d:b1:7d:d7 dev vxlan1 master br0 permanent
02:15:b8:e7:de:b3 dev veth2 master br0 permanent
33:33:00:00:00:01 dev veth2 self permanent
01:00:5e:00:00:01 dev veth2 self permanent
33:33:ff:e7:de:b3 dev veth2 self permanent
7e:55:c3:5c:c2:78 dev veth3 master br0 permanent
33:33:00:00:00:01 dev veth3 self permanent
01:00:5e:00:00:01 dev veth3 self permanent
33:33:ff:5c:c2:78 dev veth3 self permanent
72:95:ab:a1:6a:87 dev veth4 master br0 permanent
33:33:00:00:00:01 dev veth4 self permanent
01:00:5e:00:00:01 dev veth4 self permanent
33:33:ff:a1:6a:87 dev veth4 self permanent


# ARP and routing tables. Note that an overlay network only routes traffic for that network. It only has a single route that matches the subnet of that network.

/ # ip neigh show
/ # ip route
10.0.1.0/24 dev br0  proto kernel  scope link  src 10.0.1.1

# Looks like the arp table is flushed. Let's ping some of the containers on this network.

/ # ping 10.0.1.4
PING 10.0.1.4 (10.0.1.4) 56(84) bytes of data.
64 bytes from 10.0.1.4: icmp_seq=1 ttl=64 time=0.207 ms
64 bytes from 10.0.1.4: icmp_seq=2 ttl=64 time=0.087 ms
^C
--- 10.0.1.4 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 0.087/0.147/0.207/0.060 ms

/ # ip neigh show
10.0.1.4 dev br0 lladdr 02:42:0a:00:01:04 REACHABLE

# and using bridge-utils to show interfaces of the overlay network local bridge.

/ # brctl show
bridge name    bridge id        STP enabled    interfaces
br0        8000.0215b8e7deb3    no        vxlan1
                            veth2
                            veth3
                            veth4

Feedback + Contribution

Feel free to provide feedback and contribute networking troubleshooting tools and use-cases by opening PRs.

Docker Pull Command
Owner
nicolaka

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