Sublog-http NPM

sublog-http

A microservice to subscribe to a Redis pubsub channel, and serve messages via HTTP.

Example problem description

This service is intended for a personal requirement to subscribe to logging messages published via Redis. These are arrays published via pubsub.

redis-cli publish 'logger:mylogger' '["info", {"name": "evanx"}]'

where we might subscribe in the terminal as follows:

redis-cli psubscribe 'logger:*'

where we see the messages in the console as follows:

Reading messages... (press Ctrl-C to quit)
1) "psubscribe"
2) "logger:*"
3) (integer) 1
1) "pmessage"
2) "logger:*"
3) "logger:mylogger"
4) "[\"info\", {\"name\": \"evanx\"}]"

However we want to pipe to a command-line JSON formatter to enjoy a more readable rendering:

[
  "info",
  {
    "name": "evanx"
  }
]

We found that redis-cli psubscribe didn't suit that use case, e.g. piping to jq or python -mjson.tool to format the JSON.

Incidently see https://github.com/evanx/sub-push where we transfer messages to a list, brpop and then pipe to jq as an initial work-around.

Also see https://github.com/evanx/sub-write to subscribe and write to stdout with optional JSON formatting.

However it seemed like a good idea to use a browser to render the logging messages, even for local viewing, which prompted the development of this sublog-http service.

Implementation

The essence of the implementation is as follows:

async function start() {
    sub.on('message', (channel, message) => {
        if (process.env.NODE_ENV !== 'production') {
            console.log({channel, message});
        }
        state.messages.splice(0, 0, JSON.parse(message));
        state.messages = state.messages.slice(0, 10);
    });
    sub.subscribe(config.subscribeChannel);
    return startHttpServer();
}

where we keep a list of the last 10 messages in reverse order by splicing incoming messages into the head of the array.

We publish these messages via HTTP using Koa:

async function startHttpServer() {
    api.get('/', async ctx => {
        if (/(Mobile|curl)/.test(ctx.get('user-agent'))) {
            ctx.body = JSON.stringify(state.messages, null, 2);
        } else {
            ctx.body = state.messages;
        }
    });
    app.use(api.routes());
    app.use(async ctx => {
       ctx.statusCode = 404;
    });
    state.server = app.listen(config.httpPort);
}

where we format the JSON for mobile browsers i.e. without JSON formatting extensions.

evans@eowyn:~$ curl -s -I localhost:8080
HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8

Note that config is populated from environment variables as follows:

const config = ['subscribeChannel', 'httpPort', 'redisHost'].reduce((config, key) => {
    if (process.env[key] === '') {
        throw new Error('empty config ' + key);
    } else if (process.env[key]) {
        config[key] = process.env[key];
    } else if (!config[key]) {
        throw new Error('missing config ' + key);
    }
    return config;
}, {
    redisHost: '127.0.0.1'
});

where we default redisHost to localhost

Note that we check that an environment variable is not empty, for safety sake.

For example the following command line runs this service to subscribe to channel logger:mylogger and serve the JSON messages via port 8888

subscribeChannel=logger:mylogger httpPort=8888 npm start

screenshot

Incidently, some sample Node code for a client logger that publishes via Redis:

const createRedisLogger = (client, loggerName) =>
['debug', 'info', 'warn', 'error'].reduce((logger, level) => {
    logger[level] = function() {
        if (!client || client.ended === true) { // Redis client ended
        } else if (level === 'debug' && process.env.NODE_ENV === 'production') {
        } else {
            const array = [].slice.call(arguments);
            const messageJson = JSON.stringify([
                level,
                ...array.map(item => {
                    if (lodash.isError(item)) {
                        return item.stack.split('\n').slice(0, 5);
                    } else {
                        return item;
                    }
                })
            ]);
            client.publish(['logger', loggerName].join(':'), messageJson);
        }
    };
    return logger;
}, {});

where the logger level is spliced as the head of the arguments array.

Note that logged errors are specially handled i.e. a slice of the stack is logged.

Later we'll publish a more sophisticated client logger with rate limiting:

    const minute = new Date().getMinutes();
    if (metric.minute !== minute) {
        if (metric.ignored > 0) {
            client.publish(['logger', loggerName].join(':'), ['warn', {ignored: metric.ignored}]);
        }
        metric.minute = minute;
        metric.count = 0;
        metric.ignored = 0;
    } else {
        metric.count++;
        if (options.minuteLimit && metric.count > options.minuteLimit) {
            metric.ignored++;
            return;
        }
    }

Docker notes

This tested on Docker 1.12 (Ubuntu 16.04) and 1.11 (Amazon Linux 2016.09)

docker -v

Docker version 1.12.1, build 23cf638
Docker version 1.11.2, build b9f10c9/1.11.2

cat /etc/issue

Ubuntu 16.04.1 LTS
Amazon Linux AMI release 2016.09

Build application container

Let's build our application container:

docker build -t sublog-http:test https://github.com/evanx/sublog-http.git

where the image is named and tagged as sublog-http:test

Alternatively git clone and npm install and build from local dir e.g. if you wish to modify the Dockerfile

git clone https://github.com/evanx/sublog-http.git &&
  cd sublog-http && npm install &&
  docker build -t sublog-http:test .

where the default Dockerfile is as follows:

FROM mhart/alpine-node
ADD package.json .
RUN npm install
ADD src .
ENV httpPort 8080
EXPOSE 8080
CMD ["node", "--harmony-async-await", "src/index.js"]

where we ADD package.json and RUN npm install first before ADD src - so that if the source has changed but not package.json then the cached intermediate image after npm install is stil usable for a fast rebuild.

Run on host network

Using the latest Docker version or 1.12, we run on the host's network i.e. using the host's Redis instance:

docker run --network=host -e NODE_ENV=test \
  -e subscribeChannel=logger:mylogger -e httpPort=8088 -d sublog-http:test

where we configure its port to 8088 to test, noting:

although by default the port is 8080 and that is exposed via the Dockerfile
as the network is a host bridge, so the reconfigured httpPort is accessible on the host

This container can be checked as follows:

docker ps to see if actually started, otherwise omit -d to debug.
netstat -ntl to see that a process is listening on port 8088
http://localhost:8088 via curl or browser

Ensure that Redis is running on the host i.e. localhost port 6379

Test message

We can publish a test logging message as follows:

redis-cli publish logger:mylogger '["info", "test message"]'

HTTP fetch:

curl -s http://localhost:8088 | python -mjson.tool

Sample output:

[
    [
        "11:45",
        "info",
        "test message"
    ],
    [
        "11:43",
        "debug",
        "subscribeChannel",
        "logger:mylogger"
    ]
]

Bridge network

Alternatively for Docker 1.11 without --network=host but configuring a redisHost IP number:

docker run -e NODE_ENV=test -e subscribeChannel=logger:mylogger \
  -e redisHost=$redisHost -d sublog-http:test

where redisHost is the IP number of the Redis instance to which the container should connect.

Note that it cannot be localhost as the context is the container which is running the HTTP service only. Nor can it be omitted as localhost is the default Redis host used by this service.

We publish a test message as follows:

redis-cli -h $redisHost publish logger:mylogger '["info", "test message"]'

where naturally we must specify the same redisHost to which the service connects i.e. not the default localhost unless its external IP number was provided to the service, and even then rather use that to test.

Get container ID, IP address, and curl:

sublogContainer=`docker ps -q -f ancestor=sublog-http:test | head -1`
sublogHost=`docker inspect --format '{{ .NetworkSettings.Networks.bridge.IPAddress }}' $sublogContainer`
echo $sublogHost
curl -s http://$sublogHost:8080 | python -mjson.tool

Note that in this case the port will be the 8080 default configured and exposed in the Dockerfile

Incidently we can kill all containers by our image name as follows:

ids=`docker ps -q -f ancestor=sublog-http:test`
[ -n "$ids" ] && docker kill $ids

Altogether:

if [ -n "$redisHost" ]
then    
  ids=`docker ps -q -f ancestor=sublog-http:test`
  [ -n "$ids" ] && docker kill $ids
  docker run -e NODE_ENV=test -e subscribeChannel=logger:mylogger \
    -e redisHost=$redisHost -d sublog-http:test
  sleep 1
  redis-cli -h $redisHost publish logger:mylogger '["info", "test message"]'
  sublogContainer=`docker ps -q -f ancestor=sublog-http:test`
  if [ -n "$sublogContainer" ]
  then
    sublogHost=`
      docker inspect --format '{{ .NetworkSettings.Networks.bridge.IPAddress }}' $sublogContainer`
    echo $sublogHost
    curl -s http://$sublogHost:8080 | python -mjson.tool
    docker kill $sublogContainer
  fi
fi

Isolated Redis container and network

In this example we create an isolated network:

docker network create --driver bridge redis

We can create a Redis container named redis-logger as follows

docker run --network=redis --name redis-logger -d redis

We query its IP number and store in shell environment variable loggerHost

loggerHost=`docker inspect --format '{{ .NetworkSettings.Networks.redis.IPAddress }}' redis-logger`

which we can debug via

echo $loggerHost

to see that set e.g. to 172.18.0.2

Finally we run our service container:

docker run --network=redis --name sublog-http-mylogger \
  -e NODE_ENV=test -e redisHost=$loggerHost -e subscribeChannel=logger:mylogger -d sublog-http:test

where we configure redisHost for the redis-logger container via environment variable.

Note that we:

use the redis isolated network bridge for the redis-logger container
configure subscribeChannel to logger:mylogger via environment variable
name this container sublog-http-mylogger
use the previously built image sublog-http:test

Get its IP address:

myloggerHttpServer=`
  docker inspect --format '{{ .NetworkSettings.Networks.redis.IPAddress }}' sublog-http-mylogger
`

Print its URL:

echo "http://$myloggerHttpServer:8080"

Curl test:

curl -s $myloggerHttpServer:8080 | python -mjson.tool

Related projects

See

https://github.com/evanx/sub-push - subscribe to Redis pubsub channel and transfer messages to a Redis list
https://github.com/evanx/sub-write - subscribe to Redis pubsub channel and write to stdout with optional JSON formatting

We plan to publish microservices that similarly subscribe, but with purpose-built rendering for logging messages e.g. error messages coloured red.

Watch

https://github.com/evanx/sublog-console

bluebird koa koa-bodyparser koa-router lodash redis

@infinitebrahmanuniverse/nolb-subl @everything-registry/sub-chunk-2844

0.0.1

9 years ago