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What you need before writing code
- An Active LTS release of Node.js, as recommended in AWS’s Node.js guidance.
- An AWS identity whose permissions allow the intended
s3:PutObjectoperation on the target bucket and key prefix. - The bucket name and its Region. Configure that Region explicitly in deployment rather than relying on a developer machine’s default.
- Packages installed in your project:
npm install pdfkit @aws-sdk/client-s3 @aws-sdk/lib-storageUse only the packages needed by your chosen transfer path. Keep credentials out of source control; the AWS SDK can use its standard credential provider chain (environment variables, role credentials and local AWS configuration).
Generate a PDF and upload a buffer with PutObject
PDFKit’s PDFDocument is a readable Node.js stream. It does not write a complete file until you call doc.end(). The following self-contained ES module creates a simple report, collects the emitted chunks, and uploads the finished bytes.
import PDFDocument from "pdfkit";
import { S3Client, PutObjectCommand } from "@aws-sdk/client-s3";
const region = process.env.AWS_REGION;
const bucket = process.env.PDF_BUCKET;
const key = process.env.PDF_KEY ?? `reports/report-${Date.now()}.pdf`;
if (!region || !bucket) {
throw new Error("AWS_REGION and PDF_BUCKET are required");
}
function makePdfBuffer() {
return new Promise((resolve, reject) => {
const doc = new PDFDocument();
const chunks = [];
doc.on("data", chunk => chunks.push(chunk));
doc.once("end", () => resolve(Buffer.concat(chunks)));
doc.once("error", reject);
doc.fontSize(22).text("Monthly report", { align: "center" });
doc.moveDown().fontSize(12).text(`Generated: ${new Date().toISOString()}`);
doc.moveDown().text("This PDF was generated by Node.js and stored in Amazon S3.");
doc.end();
});
}
const pdfBuffer = await makePdfBuffer();
const s3 = new S3Client({ region });
try {
const result = await s3.send(new PutObjectCommand({
Bucket: bucket,
Key: key,
Body: pdfBuffer,
ContentType: "application/pdf"
}));
console.log({ bucket, key, etag: result.ETag });
} catch (error) {
console.error("S3 PDF upload failed", {
name: error.name,
message: error.message,
bucket,
key
});
throw error;
}Run this as an ES module (for example, set "type": "module" in package.json) and provide AWS_REGION, PDF_BUCKET, and optionally PDF_KEY. A successful send means the S3 request completed; the returned ETag is useful for logging but should not automatically be treated as a content hash for every upload mode.
Why these request fields matter
Bucketidentifies the destination bucket.Keyis the complete object name, including any prefix such asreports/.Bodyaccepts the generated bytes.ContentType: "application/pdf"lets browsers and downstream services handle the object as a PDF.
Choose an intentional key and keep the bucket private unless your application’s access policy specifically requires public access. A PDF being easy to retrieve is not a reason to make an entire bucket or object public.
Do you need to save the PDF to disk?
No. You can upload a buffer directly, or use a stream-oriented design. The right choice depends on document size, memory limits, retry requirements and operational complexity.
| Approach | Peak memory | Disk use | When it fits | Main concern |
|---|---|---|---|---|
Buffer plus PutObject |
PDF bytes are held in memory | None | Small or moderate reports and simple workers | A large PDF can pressure the process heap |
| Temporary file plus read stream | Small application buffer | Temporary file required | When memory is constrained and local ephemeral storage is available | Clean up files on success, failure and cancellation |
| PDFKit stream plus multipart helper | Designed to avoid one giant buffer | None in a direct pipeline | Large output or long-running generation | More involved stream, retry and backpressure handling |
The table describes engineering trade-offs, not a published performance benchmark. Test with your document sizes and runtime limits.
Upload a generated stream with multipart support
A PDFKit stream can feed an upload, but do not assume that two readable-stream interfaces compose correctly without testing. The producer must be finalized, stream errors must reject the upload, backpressure must be respected, and the upload promise must be awaited. AWS identifies @aws-sdk/lib-storage as the SDK v3 multipart-upload helper.
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import PDFDocument from "pdfkit";
import { S3Client } from "@aws-sdk/client-s3";
import { Upload } from "@aws-sdk/lib-storage";
const doc = new PDFDocument();
const s3 = new S3Client({ region: process.env.AWS_REGION });
const upload = new Upload({
client: s3,
params: {
Bucket: process.env.PDF_BUCKET,
Key: "reports/large-report.pdf",
Body: doc,
ContentType: "application/pdf"
}
});
upload.on("httpUploadProgress", progress => {
console.log({ loaded: progress.loaded, total: progress.total });
});
const uploadPromise = upload.done();
doc.on("error", error => upload.abort().catch(() => {}));
doc.fontSize(18).text("Large report");
// Add the rest of the document here, then finalize the readable stream.
doc.end();
try {
await uploadPromise;
console.log("PDF upload complete");
} catch (error) {
console.error("Multipart PDF upload failed", error);
throw error;
}This pattern is intentionally a starting point rather than a guarantee for every installed version. Verify the exact SDK and PDFKit versions, test a forced stream error, and confirm that cancellation does not leave an incomplete multipart upload. If that complexity is not justified, write to a temporary file and upload a read stream, or use the buffer pattern.
Temporary-file workflow
Staging is often the easiest compromise for a large report: PDFKit writes to a temporary file, the file is opened as a read stream, and the stream is passed to the S3 operation or multipart helper. Use a unique path, restrict its permissions, remove it in a finally block, and account for the container or serverless environment’s ephemeral-storage limit. Do not expose the temporary path or document contents in ordinary logs.
Region, credentials and integrity
Configure the bucket’s Region
Construct S3Client with the Region that actually contains the bucket. A wrong Region can produce redirects or authorization-looking failures. Make the value an environment setting in each deployment environment, not an accidental value inherited from a laptop.
Use the AWS credential chain safely
Prefer workload roles (for example, a task or instance role) in AWS-hosted environments. For local development, use the standard AWS configuration or environment variables. Never put access keys in a PDF, a repository, a client-side bundle or a URL. Grant only the bucket and key-prefix permissions the worker needs.
Understand checksum behavior
AWS documents default CRC32 upload checksum calculation for AWS SDK for JavaScript v3.729.0 and later when no precalculated checksum or alternate algorithm is selected. This is version- and configuration-dependent. Pin and review your SDK version, and confirm the effective checksum settings before relying on that behavior as an integrity control.
Make completion and retries reliable
- Call
doc.end()exactly once. Calling it too early truncates the document; never calling it leaves the upload waiting. - Attach handlers for both PDF-generation and S3 errors. A PDF stream error must fail the job, not merely print a warning.
- Await
s3.send(...)orupload.done()before acknowledging a queue message, returning success to an API caller or deleting source data. - Use deterministic, collision-resistant keys. If a retry must not overwrite an existing report, include a report ID or UUID and enforce that policy in your application.
- Retry transient AWS failures with bounded backoff, but do not blindly retry credential, permission, validation or malformed-key errors.
- For multipart jobs, make sure aborted uploads are cleaned up and that the worker can resume or safely create a new key according to your idempotency design.
Troubleshooting common failures
AccessDenied
The identity lacks permission, a bucket policy denies the request, or encryption requirements are not satisfied. Check the effective role, bucket policy, key prefix and any required server-side-encryption headers. Do not solve this by making the object public.
NoSuchBucket or a Region redirect
Confirm the bucket name exactly and set AWS_REGION to the bucket’s Region. Avoid silently falling back to a local profile’s Region.
The object is empty or unreadable
Ensure PDFKit received all content before doc.end(), collect all buffer chunks until the end event, and set ContentType. In a stream pipeline, verify that the producer’s error reaches the upload promise.
The process runs out of memory
Stop buffering the entire PDF. Stage to a temporary file or use a tested multipart stream. Also check whether multiple reports are being generated concurrently and cap worker concurrency.
The upload hangs
A stream may never have been finalized, or an error may not be connected to the upload. Call doc.end(), attach error handlers before starting generation, and inspect whether the upload promise is actually awaited.
EntityTooLarge or a size-limit error
Use the upload method appropriate to the output size, such as the SDK v3 multipart helper, and verify the current service and operation limits for your selected method. Do not rely on a limit shown in an old sample without checking its applicability.
Retries create duplicate reports
Use an application-level report ID in the key, record job state separately, and decide whether a retry should overwrite, verify, or create a new object. S3 success alone does not tell your application whether a prior worker attempt also completed.
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Generate the PDF with a single call, then pass the response bytes to the same S3 PutObjectCommand shown above:
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Operational checklist
- PDF generation completed and the stream was ended.
- Bucket, key and Region were validated from configuration.
- Credentials use a least-privilege identity.
ContentTypeisapplication/pdf.- The selected buffer, temporary-file or multipart path matches the document size.
- Generation and upload errors are observable without logging secrets or document contents.
- The job reports success only after the upload promise resolves.
- Access to the resulting object follows your application’s security policy.
Frequently Asked Questions
Can I upload a PDF stream directly to S3?
Yes. PDFKit exposes a readable Node.js stream, and AWS SDK v3’s multipart helper can consume a stream, but test error propagation, finalization and backpressure with your installed versions.
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Collect PDFKit chunks into a Buffer and send it as Body in PutObjectCommand with ContentType set to application/pdf.
Will S3 automatically make my PDF downloadable?
S3 stores the object; retrieval and download behavior depend on your bucket policy, object permissions and response headers. Keep access private unless your application explicitly requires otherwise.
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