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.