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    2.1.2 • Public • Published


    Setup a fake Cloudwatch logs server for testing purposes


    const AWS = require('aws-sdk')
    const path = require('path')
    const { FakeCloudwatchLogs } = require('fake-cloudwatch-logs')
    const ACCESS_KEY = '123'
    async function test() {
      const region = 'us-east-1'
      const server = new FakeCloudwatchLogs({
        port: 0,
        cachePath: path.join(__dirname, 'cw-fixtures')
      server.populateGroups(ACCESS_KEY, region, [...])
      server.populateStreams(ACCESS_KEY, region, 'my-group', [...])
        ACCESS_KEY, region, 'my-group', 'my-stream', [...]
      await server.populateFromCache()
      await server.bootstrap()
      const cw = new AWS.CloudwatchLogs({
        region: region,
        endpoint: `http://${server.hostPort}`,
        sslEnabled: false,
        accessKey: ACCESS_KEY,
        secretAccessKey: 'abc'
      const groups = await cw.describeLogGroups().promise()
      // Should be groups you populated or loaded from disk cache
      console.log('the groups', groups.logGroups)
      const events = await cw.getLogEvents({
        logGroupName: 'my-group',
        logStreamName: 'my-stream'
      // Should be events you populated.
      console.log('the events', events.events)
      await server.close()
    process.on('unhandledRejection', (err) => { throw err })


    Currently this fake-cloudwatch-logs module supports various read APIs like describe log groups, describe streams and fetching log events.

    It also supports APIs designed for making a read-only copy of production data cached on disks. This allows for using fixture data for local development and integration tests.

    The other functionality can be added in the future, as needed.

    The API that are supported are :

    • DescribeLogGroups
    • DescribeLogStreams
    • GetLogEvents

    Recommended testing approach

    Create the FakeCloudwatchLogs server in your test harness. Then configure your aws client to point to the endpoint.

    You can call populate methods to populate mock data into the fake cloudwatch server.

    Recommended local approach

    Create the FakeCloudwatchLogs server on some HTTP port of your choice.

    I recommend copying the scripts/cache-from-prod.js into your application, this will cache production data into a fixtures directory.

    You can configure the FakeCloudwatchLogs to fetch that fixtures data into memory and then configure your website or application or server to point to the FakeCloudwatchLogs on whatever port you choose.

    Here is an example snippet from the script

    'use strict'
    const path = require('path')
    const AWS = require('aws-sdk')
    const FakeCloudWatchLogs =
    async function main () {
      const fakeCW = new FakeCloudWatchLogs({
        cachePath: path.join(__dirname, '..', 'fixtures')
      await fakeCW.populateFromCache()
      // 'all' regions or ['us-east-1']
      // await fakeCW.fetchAndCache(AWS, ['us-east-1'])
      await fakeCW.fetchAndCache(AWS, 'all')
    main().then(null, (err) => {
      process.nextTick(() => { throw err })

    Docs :

    const server = new FakeCloudwatchLogs(options)

    Creates a fake Cloudwatch logs server listening on the port your specified.

    • options.port; port to lsiten on, defaults to 0
    • options.cachePath; the location to read/write fixtures to.

    await server.bootstrap()

    Starts the server. After this method completes the field server.hostPort is available and can be used to access the actual listening port of the server if you choose to listen on port 0.

    await server.close()

    Closes the http server.

    server.populateGroups(accessKey, region, groups)

    Adds groups to the in-memory server. The group must be a valid LogGroup

    const group = server.makeLogGroup(name)

    server.populateStreams(accessKey, region, groupName, streams)

    Adds streams to the in-memory server that belong to the groupName. The streams must be a valid LogStream

    const stream = server.makeLogStream(name)

    server.populateEvents(accessKey, region, groupName, streamName, events)

    Adds events to the in-memory server that belong to the groupName and the streamName. The events must be a valid OutputLogEvent

    const event = server.makeLogEvent()

    await server.populateFromCache()

    This will have the server fetch groups, streams & events from a cache on disk. This can be useful for writing tests with fixtures or for starting a local server that loads fixtures from disk.

    It's recommende you use the cacheXToDisk() methods to create the fixtures.

    await server.fetchAndCache(AWS, regions)

    If you want to fetch and cache data from production into a fixtures directory you can call fetchAndCache() with the AWS sdk and with the regions you want to cache.

    You can pass ['us-east-1'] etc as a the regions or the string 'all' if you want to fetch all regions.

    await server.cacheGroupsToDisk(cacheDir, groups)

    This will write groups to disk in the cache directory. The groups must be valid LogGroup ;

    await server.cacheStreamsToDisk(cacheDir, groupName, streams)

    This will write streams to disk in the cache directory for the groupName you specify. The streams must be valid LogStream

    await server.cacheEventsToDisk(cacheDir, groupName, streamName, events)

    This will write events to disk in the cache directory for the groupName and streamName you specify. The streams must be valid OutputLogEvent ;


    % npm install fake-cloudwatch-logs

    MIT Licensed




    npm i fake-cloudwatch-logs

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