reslack

Notifications via Redis to Slack channel via Slackbot.

Use case

We wish to send alerts for application errors to a Slack channel.

Our application services use a logger which writes errors into Redis.

Consider the following common error logging method.

    logger.error(err);

The implementation logs the latest error into Redis, according to the client ID.

    multi.hmset(`reconsole:error:${clientId}:h`, {
        time: new Date(timestamp).toISOString(),
        message: err.message
    });
    multi.sadd('reconsole:error:s', clientId);

This service will POST alerts to a Slack channel, e.g. in collaboration with reconsole.

Configuration

See lib/spec.js https://github.com/evanx/reslack/blob/master/lib/spec.js

module.exports = pkg => ({
    description: pkg.description,
    env: {
        redisHost: {
            description: 'the Redis host',
            default: 'localhost'
        },
        redisPort: {
            description: 'the Redis port',
            default: 6379
        },
        redisNamespace: {
            description: 'the Redis namespace',
            default: 'reslack'
        },
        slackUrl: {
            description: 'Slack URL',
        },
        slackChannel: {
            description: 'Slack channel',
            default: '#ops'
        },
        slackUsername: {
            description: 'Slack username',
            default: 'reslackBot'
        },
        slackIcon: {
            description: 'Slack icon emoji',
            default: 'monkey'
        },
        popDelay: {
            description: 'pop delay',
            unit: 'ms',
            default: 2000
        },
        popTimeout: {
            description: 'pop timeout',
            unit: 'ms',
            default: 2000
        }
    },
    redisK: config => ({
        reqS: {
            key: `${config.redisNamespace}:req:s`
        },
        reqQ: {
            key: `${config.redisNamespace}:req:q`
        },
        reqH: {
            key: sha => `${config.redisNamespace}:${sha}:req:h`
        },
        busyQ: {
            key: `${config.redisNamespace}:busy:q`
        },
        reqC: {
            key: `${config.redisNamespace}:req:count:h`
        },
        errorC: {
            key: `${config.redisNamespace}:error:count:h`
        }
    })
});

Docker

See Dockerfile https://github.com/evanx/reslack/blob/master/Dockerfile

FROM mhart/alpine
ADD package.json .
RUN npm install --silent
ADD lib lib
ENV NODE_ENV production
CMD ["node", "lib/index.js"]

We can build as follows:

docker build -t reslack https://github.com/evanx/reslack.git

where tagged as image reslack

Then for example, we can run on the host's Redis as follows:

docker run --network=host -e slackUrl=$SLACK_URL reslack

where --network-host connects the container to your localhost bridge. The default Redis host localhost works in that case.

Since the containerized app has access to the host's Redis instance, you should inspect the source.

Implementation

See lib/main.js https://github.com/evanx/reslack/blob/master/lib/main.js

    const sha = await client.brpoplpushAsync(redisK.reqQ, redisK.busyQ, config.popTimeout);
    const [hashes] = await multiExecAsync(client, multi => {
        multi.hgetall(redisK.reqH(sha));
        multi.hincrby(redisK.reqC, 'pop', 1);
    });
    asserto({hashes});
    const {text} = hashes;
    asserto({text});
    const payload = {
        channel: config.slackChannel,
        username: config.slackUsername,
        icon_emoji: [':', config.slackIcon, ':'].join(''),
        text
    };
    const fetchRes = await fetch(req.url, {
        url: config.slackUrl,
        method: 'POST',
        headers: {
            'content-type': 'application/x-www-form-urlencoded'
        },
        body: 'payload=' + JSON.stringify(payload).replace(/"/g, '\'')
    });
    if (fetchRes.status !== 200) {
        throw new DataError(`Status ${fetchRes.status}`, payload);
    }

Uses application archetype: https://github.com/evanx/redis-app

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