Calculating Cache Hit Ratio from fastly logs

cache-ratio.mjs

import { readdir, readFile } from 'node:fs/promises';

// Update this path to point to a directory of log files.
const logPath = './fastly-logs';
const files = await readdir(logPath);

// This map holds pairs of page name and page regex and is used to group requests into page types.
// The regex for each is tested against the url of the request in the logline 
/// You should update this map to be relevant for the requests you're interested in.
const types = new Map([
    ['home',  /^\/([?].+)?$/],
    ['static_assets',  /^\/static-assets\/.+/],
    ['recipe',  /^\/recipe\/.+/],
    ['compilation',  /^\/compilation\/.+/],
    ['article',  /^\/article\/.+/]
]);

let logLines = [];
const states = {
    'MISS-CLUSTER': 'MISS',
    'MISS-WAIT-CLUSTER': 'MISS',
    'MISS-WAIT': 'MISS',
    'HIT-CLUSTER': 'HIT',
    'HIT-SYNTH': 'HIT',
    'HIT-WAIT-CLUSTER': 'HIT',
    'HIT-STALE': 'HIT',
    'HIT-STALE-WAIT': 'HIT',
    'HIT-STALE-CLUSTER': 'HIT',
    'HIT-WAIT': 'HIT',
    'HITPASS': 'HIT'
}

for (const filename of files) {
    const rawLogs = await readFile(`${logPath}/${filename}`, 'utf-8');
    const structuredLogs = rawLogs.split('\n')
        .filter(Boolean)
        .map(ll => JSON.parse(ll))
        .map(ll => ({ path: ll.http.path, state: ll.network.server.state }))
        logLines.push(structuredLogs);
}

const totals = logLines.flat()
    .reduce((acc,next) => {
        let type;
        for (let [name, tester] of types) {
            if (next.path.match(tester)) {
                type = name;
                break;
            }
        }
        if (!type) return acc;
        const state = states[next.state] || next.state;
        if (acc[type][state]) {
            acc[type][state]++;
        } else {
            acc[type][state] = 1;
        }
        return acc;
    }, [...types.keys()].reduce((obj, page) => ({...obj, [`${page}`]: {}}), {}))

console.log(`Cache Hit Ratios:`);
Object.keys(totals).forEach(type => {
    console.log(`${type}: ${(totals[type].HIT / (totals[type].MISS + totals[type].HIT) * 100)}`);
});