NATS and Docker

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NATS and Docker
NATS Server Containerization
The NATS server is provided as a Docker image on Docker Hub that you can run using the Docker daemon. The NATS server Docker image is extremely lightweight, coming in under 10 MB in size.
​Synadia actively maintains and supports the NATS server Docker image.
Usage
To use the Docker container image, install Docker and pull the public image:
docker pull nats
Run the NATS server image:
docker run nats
By default the NATS server exposes multiple ports:
4222 is for clients.
8222 is an HTTP management port for information reporting.
6222 is a routing port for clustering.
Use -p or -P to customize.
To run a server with the ports exposed on a docker network:
First create the 'docker network' nats
docker network create nats
And start the server
docker run --name nats --network nats --rm -p 4222:4222 -p 8222:8222 nats --http_port 8222
Creating a NATS Cluster
First run a server with the ports exposed on the 'nats' docker network:
docker run --name nats --network nats --rm -p 4222:4222 -p 8222:8222 nats --http_port 8222 --cluster_name NATS --cluster nats://0.0.0.0:6222
[1] 2021/09/28 09:21:56.554756 [INF] Starting nats-server
[1] 2021/09/28 09:21:56.554864 [INF]   Version:  2.6.1
[1] 2021/09/28 09:21:56.554878 [INF]   Git:      [c91f0fe]
[1] 2021/09/28 09:21:56.554894 [INF]   Name:     NDIQLLD2UGGPSAEYBKHW3S2JB2DXIAFHMIWWRUBAX7FC4RTQX4ET2JNQ
[1] 2021/09/28 09:21:56.555001 [INF]   ID:       NDIQLLD2UGGPSAEYBKHW3S2JB2DXIAFHMIWWRUBAX7FC4RTQX4ET2JNQ
[1] 2021/09/28 09:21:56.557658 [INF] Starting http monitor on 0.0.0.0:8222
[1] 2021/09/28 09:21:56.557967 [INF] Listening for client connections on 0.0.0.0:4222
[1] 2021/09/28 09:21:56.559224 [INF] Server is ready
[1] 2021/09/28 09:21:56.559375 [INF] Cluster name is NATS
[1] 2021/09/28 09:21:56.559433 [INF] Listening for route connections on 0.0.0.0:6222
Next, start another couple of servers and point them to the seed server to make them form a cluster:
docker run --name nats-1 --network nats --rm nats --cluster_name NATS --cluster nats://0.0.0.0:6222 --routes=nats://ruser:[email protected]:6222
docker run --name nats-2 --network nats --rm nats --cluster_name NATS --cluster nats://0.0.0.0:6222 --routes=nats://ruser:[email protected]:6222
NOTE Since the Docker image protects routes using credentials we need to provide them above. Extracted from Docker image configuration​
To verify the routes are connected, you can make a request to the monitoring endpoint on /routez as follows and confirm that there are now 2 routes:
curl http://127.0.0.1:8222/routez
{
  "server_id": "NDIQLLD2UGGPSAEYBKHW3S2JB2DXIAFHMIWWRUBAX7FC4RTQX4ET2JNQ",
  "now": "2021-09-28T09:22:15.8019785Z",
  "num_routes": 2,
  "routes": [
    {
      "rid": 5,
      "remote_id": "NBRAUY3YSVFYU7BFWI2YF5VPQFGO2XCKKAHYZ7ETCMGB3SQY3FDFTYOQ",
      "did_solicit": false,
      "is_configured": false,
      "ip": "172.18.0.3",
      "port": 59092,
      "pending_size": 0,
      "rtt": "1.2505ms",
      "in_msgs": 4,
      "out_msgs": 3,
      "in_bytes": 2714,
      "out_bytes": 1943,
      "subscriptions": 35
    },
    {
      "rid": 6,
      "remote_id": "NA5STTST5GYFCD22M2I3VDJ57LQKOU35ZVWKQY3O5QRFGOPC3RFDIDVJ",
      "did_solicit": false,
      "is_configured": false,
      "ip": "172.18.0.4",
      "port": 47424,
      "pending_size": 0,
      "rtt": "1.2008ms",
      "in_msgs": 4,
      "out_msgs": 1,
      "in_bytes": 2930,
      "out_bytes": 833,
      "subscriptions": 35
    }
  ]
}
Creating a NATS Cluster with Docker Compose
It is also straightforward to create a cluster using Docker Compose. Below is a simple example that uses a network named nats to create a full mesh cluster.
version: "3.5"
services:
  nats:
    image: nats
    ports:
      - "8222:8222"
    command: "--cluster_name NATS --cluster nats://0.0.0.0:6222 --http_port 8222 "
    networks: ["nats"]
  nats-1:
    image: nats
    command: "--cluster_name NATS --cluster nats://0.0.0.0:6222 --routes=nats://ruser:[email protected]:6222"
    networks: ["nats"]
    depends_on: ["nats"]
  nats-2:
    image: nats
    command: "--cluster_name NATS --cluster nats://0.0.0.0:6222 --routes=nats://ruser:[email protected]:6222"
    networks: ["nats"]
    depends_on: ["nats"]
​
networks:
  nats:
    name: nats
Now we use Docker Compose to create the cluster that will be using the nats network:
docker-compose -f nats-cluster.yaml up
[+] Running 3/3
 ⠿ Container xxx_nats_1    Created
 ⠿ Container xxx_nats-1_1  Created
 ⠿ Container xxx_nats-2_1  Created
Attaching to nats-1_1, nats-2_1, nats_1
nats_1    | [1] 2021/09/28 10:42:36.742844 [INF] Starting nats-server
nats_1    | [1] 2021/09/28 10:42:36.742898 [INF]   Version:  2.6.1
nats_1    | [1] 2021/09/28 10:42:36.742913 [INF]   Git:      [c91f0fe]
nats_1    | [1] 2021/09/28 10:42:36.742929 [INF]   Name:     NCZIIQ6QT4KT5K5WBP7H2RRBM4MSYD4C2TVSRZOZN57EHX6VTF4EWXAU
nats_1    | [1] 2021/09/28 10:42:36.742954 [INF]   ID:       NCZIIQ6QT4KT5K5WBP7H2RRBM4MSYD4C2TVSRZOZN57EHX6VTF4EWXAU
nats_1    | [1] 2021/09/28 10:42:36.745289 [INF] Starting http monitor on 0.0.0.0:8222
nats_1    | [1] 2021/09/28 10:42:36.745737 [INF] Listening for client connections on 0.0.0.0:4222
nats_1    | [1] 2021/09/28 10:42:36.750381 [INF] Server is ready
nats_1    | [1] 2021/09/28 10:42:36.750669 [INF] Cluster name is NATS
nats_1    | [1] 2021/09/28 10:42:36.751444 [INF] Listening for route connections on 0.0.0.0:6222
nats-1_1  | [1] 2021/09/28 10:42:37.709888 [INF] Starting nats-server
nats-1_1  | [1] 2021/09/28 10:42:37.709977 [INF]   Version:  2.6.1
nats-1_1  | [1] 2021/09/28 10:42:37.709999 [INF]   Git:      [c91f0fe]
nats-1_1  | [1] 2021/09/28 10:42:37.710023 [INF]   Name:     NBHTXXY3HYZVPXITYQ73BSDA5CQZINTKYRM23XFI46RWWTTUP5TAXQMB
nats-1_1  | [1] 2021/09/28 10:42:37.710042 [INF]   ID:       NBHTXXY3HYZVPXITYQ73BSDA5CQZINTKYRM23XFI46RWWTTUP5TAXQMB
nats-1_1  | [1] 2021/09/28 10:42:37.711646 [INF] Listening for client connections on 0.0.0.0:4222
nats-1_1  | [1] 2021/09/28 10:42:37.712197 [INF] Server is ready
nats-1_1  | [1] 2021/09/28 10:42:37.712376 [INF] Cluster name is NATS
nats-1_1  | [1] 2021/09/28 10:42:37.712469 [INF] Listening for route connections on 0.0.0.0:6222
nats_1    | [1] 2021/09/28 10:42:37.718918 [INF] 172.18.0.4:52950 - rid:4 - Route connection created
nats-1_1  | [1] 2021/09/28 10:42:37.719906 [INF] 172.18.0.3:6222 - rid:4 - Route connection created
nats-2_1  | [1] 2021/09/28 10:42:37.731357 [INF] Starting nats-server
nats-2_1  | [1] 2021/09/28 10:42:37.731518 [INF]   Version:  2.6.1
nats-2_1  | [1] 2021/09/28 10:42:37.731531 [INF]   Git:      [c91f0fe]
nats-2_1  | [1] 2021/09/28 10:42:37.731543 [INF]   Name:     NCG6UQ2N3IHE6OS76TL46RNZBAPHNUCQSA64FDFHG5US2LLJOQLD5ZK2
nats-2_1  | [1] 2021/09/28 10:42:37.731554 [INF]   ID:       NCG6UQ2N3IHE6OS76TL46RNZBAPHNUCQSA64FDFHG5US2LLJOQLD5ZK2
nats-2_1  | [1] 2021/09/28 10:42:37.732893 [INF] Listening for client connections on 0.0.0.0:4222
nats-2_1  | [1] 2021/09/28 10:42:37.733431 [INF] Server is ready
nats-2_1  | [1] 2021/09/28 10:42:37.733491 [INF] Cluster name is NATS
nats-2_1  | [1] 2021/09/28 10:42:37.733835 [INF] Listening for route connections on 0.0.0.0:6222
nats_1    | [1] 2021/09/28 10:42:37.740860 [INF] 172.18.0.5:54616 - rid:5 - Route connection created
nats-2_1  | [1] 2021/09/28 10:42:37.741557 [INF] 172.18.0.3:6222 - rid:4 - Route connection created
nats-1_1  | [1] 2021/09/28 10:42:37.743981 [INF] 172.18.0.5:6222 - rid:5 - Route connection created
nats-2_1  | [1] 2021/09/28 10:42:37.744332 [INF] 172.18.0.4:40250 - rid:5 - Route connection created
Testing the Clusters
Now, the following should work: make a subscription on one of the nodes and publish it from another node. You should be able to receive the message without problems.
docker run --network nats --rm -it synadia/nats-box
Inside the container
nats sub -s nats://nats:4222 hello &
nats pub -s "nats://nats-1:4222" hello first
nats pub -s "nats://nats-2:4222" hello second
Also stopping the seed node to which the subscription was done, should trigger an automatic failover to the other nodes:
docker-compose -f nats-cluster.yaml stop nats
Output extract
... 
16e55f1c4f3c:~# 10:47:28 Disconnected due to: EOF, will attempt reconnect
10:47:28 Disconnected due to: EOF, will attempt reconnect
10:47:28 Reconnected [nats://172.18.0.4:4222]
Publishing again will continue to work after the reconnection:
nats pub -s "nats://nats-1:4222" hello again
nats pub -s "nats://nats-2:4222" hello again
Tutorial
See the NATS Docker tutorial for more instructions on using the NATS server Docker image.
Running a NATS service - Previous
Environmental considerations
Tutorial
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Outline
NATS Server Containerization
Usage
Creating a NATS Cluster
Creating a NATS Cluster with Docker Compose
Testing the Clusters
Tutorial