forgejo/lib/constructs/backup-verification.ts

import * as cdk from "aws-cdk-lib";
import * as cloudwatch from "aws-cdk-lib/aws-cloudwatch";
import * as events from "aws-cdk-lib/aws-events";
import * as events_targets from "aws-cdk-lib/aws-events-targets";
import * as iam from "aws-cdk-lib/aws-iam";
import * as lambda from "aws-cdk-lib/aws-lambda";
import * as logs from "aws-cdk-lib/aws-logs";
import * as s3 from "aws-cdk-lib/aws-s3";
import { PythonFunction } from "@aws-cdk/aws-lambda-python-alpha";
import { Construct } from "constructs";

interface BackupVerificationProps {
  sourceBucket: s3.IBucket;
  replicaBucketName: string;
  gcsBucket: string;
  gcsSaSecretName: string;
  slackWebhookSecretName: string;
}

export class BackupVerification extends Construct {
  public readonly functionArn: string;

  constructor(scope: Construct, id: string, props: BackupVerificationProps) {
    super(scope, id);

    const fn = new PythonFunction(this, "Function", {
      functionName: "forgejo-backup-verification",
      entry: "lambda/backup-verification",
      runtime: lambda.Runtime.PYTHON_3_12,
      architecture: lambda.Architecture.ARM_64,
      handler: "handler",
      index: "app.py",
      memorySize: 512,
      ephemeralStorageSize: cdk.Size.gibibytes(4),
      timeout: cdk.Duration.minutes(5),
      environment: {
        SOURCE_BUCKET: props.sourceBucket.bucketName,
        REPLICA_BUCKET: props.replicaBucketName,
        GCS_BUCKET: props.gcsBucket,
        GCS_SA_SECRET_NAME: props.gcsSaSecretName,
        SLACK_WEBHOOK_SECRET_NAME: props.slackWebhookSecretName,
      },
      logRetention: logs.RetentionDays.TWO_MONTHS,
    });

    props.sourceBucket.grantRead(fn);

    fn.addToRolePolicy(
      new iam.PolicyStatement({
        actions: ["s3:ListBucket", "s3:GetObject"],
        resources: [
          `arn:aws:s3:::${props.replicaBucketName}`,
          `arn:aws:s3:::${props.replicaBucketName}/*`,
        ],
      })
    );

    const account = cdk.Stack.of(this).account;
    const region = cdk.Stack.of(this).region;

    fn.addToRolePolicy(
      new iam.PolicyStatement({
        actions: ["secretsmanager:GetSecretValue"],
        resources: [
          `arn:aws:secretsmanager:${region}:${account}:secret:${props.gcsSaSecretName}-*`,
          `arn:aws:secretsmanager:${region}:${account}:secret:${props.slackWebhookSecretName}-*`,
        ],
      })
    );

    fn.addToRolePolicy(
      new iam.PolicyStatement({
        actions: ["ec2:DescribeSnapshots"],
        resources: ["*"],
      })
    );

    new events.Rule(this, "DailyCheck", {
      ruleName: "forgejo-backup-daily-check",
      schedule: events.Schedule.cron({ hour: "8", minute: "0" }),
      targets: [
        new events_targets.LambdaFunction(fn, {
          event: events.RuleTargetInput.fromObject({ mode: "daily" }),
        }),
      ],
    });

    new events.Rule(this, "MonthlyRestoreTest", {
      ruleName: "forgejo-backup-monthly-restore-test",
      schedule: events.Schedule.cron({
        hour: "9",
        minute: "0",
        day: "1",
      }),
      targets: [
        new events_targets.LambdaFunction(fn, {
          event: events.RuleTargetInput.fromObject({ mode: "restore-test" }),
        }),
      ],
    });

    // Errors alarm: only fires when the function actually runs and errors.
    // The function runs once daily, so for ~23h there is no data. Treating
    // missing data as BREACHING flipped this alarm OK->ALARM every day around
    // 11:01 UTC even though no error ever occurred. NOT_BREACHING means "no
    // data = no errors = healthy"; the separate not-running alarm below covers
    // the "verification never ran" case.
    new cloudwatch.Alarm(this, "ErrorAlarm", {
      alarmName: "forgejo-backup-verification-errors",
      alarmDescription: "Backup verification Lambda is failing — Slack notifications may not be firing",
      metric: fn.metricErrors({ period: cdk.Duration.hours(1) }),
      threshold: 1,
      evaluationPeriods: 1,
      treatMissingData: cloudwatch.TreatMissingData.NOT_BREACHING,
      comparisonOperator: cloudwatch.ComparisonOperator.GREATER_THAN_OR_EQUAL_TO_THRESHOLD,
    });

    // Not-running alarm: fires if the daily verification did not invoke at all
    // in a 24h window. This is the real "missing run" guard that the errors
    // alarm's BREACHING setting was previously (and incorrectly) providing.
    new cloudwatch.Alarm(this, "NotRunningAlarm", {
      alarmName: "forgejo-backup-verification-not-running",
      alarmDescription: "Backup verification Lambda has not run in the last 24h — daily verification may be broken",
      metric: fn.metricInvocations({
        period: cdk.Duration.hours(24),
        statistic: cloudwatch.Stats.SUM,
      }),
      threshold: 1,
      evaluationPeriods: 1,
      treatMissingData: cloudwatch.TreatMissingData.BREACHING,
      comparisonOperator: cloudwatch.ComparisonOperator.LESS_THAN_THRESHOLD,
    });

    this.functionArn = fn.functionArn;
  }
}