Any HTML→PDF gem that supports modern CSS (flex/grid) and works on Ruby 2.5.1 + Rails 5.0.7.2?

Background

I have an existing Rails 5.0.7.2 app running on Ruby 2.5.1. In several places I generate invoices as HTML (I build a full HTML string by replacing template tags server-side) and convert to PDF for download.

Problem

WickedPDF (wkhtmltopdf) is currently used. It generally works, but wkhtmltopdf's old WebKit engine doesn't support modern CSS (flexbox / grid) reliably. I replaced many layout bits with tables/floats to try to make it stable, but when invoice content gets long the PDF layout still breaks (columns jump, bottom section moves to next page, etc).

I want a modern engine that renders the same HTML/CSS as Chrome (so flex/grid work and page-breaks behave like in the browser). But my app uses Ruby 2.5.1 and Rails 5.0.7.2, so many modern gems are not compatible.

What I tried (summary)

1. WickedPDF + wkhtmltopdf

Works with Ruby 2.5.1.
Pros: no Ruby upgrade required, already in project.
Cons: old WebKit — flex/grid / page-breaks unreliable.

1. Grover (Puppeteer/Headless Chrome wrapper)

Goal: use headless Chrome so rendering matches browser.
Issues encountered:
Grover::DependencyError: Cannot find module 'puppeteer' → installed puppeteer via npm.
Chromium failed to run due to OS libraries (libnspr4.so missing) — fixed by installing system packages (Ubuntu 24.04 t64 libs).
PATH issues inside Rails (Spring/asdf) — fixed by exporting asdf shims into Rails env.
Final blocking error: NoMethodError: undefined method 'pack' for nil:NilClass from grover/processor.rb. Investigating versions revealed Grover >= 1.1 requires Ruby ≥ 2.7 and newer Grover versions are incompatible with Ruby 2.5. Attempts to find a compatible Grover version led to version constraints or runtime errors (pack nil or other incompatibilities). Conclusion: Grover is not a viable option unless I upgrade Ruby.

1. prawn + prawn-html

Prawn itself is fine on Ruby 2.5.1 but prawn-html requires Ruby >= 2.6, so it won't install in my environment. Using raw Prawn would require me to rewrite the whole invoice layout in Prawn DSL (workable but heavy).

1. pdfkit / wkhtmltopdf

Same underlying engine as WickedPDF, so it doesn't solve the CSS/flexbox problem.

1. Tried multiple Grover versions

Older 0.x or 1.x variants either lack needed capabilities or require newer Ruby. The project’s Ruby limits all modern Grover versions.

My constraints

• I cannot upgrade Ruby/Rails right now (legacy app + constraints).
• I want to keep using the generated HTML (no time to rewrite invoice into Prawn DSL).
• Prefer a solution that: a) renders modern CSS (flex/grid), b) works without forcing a Ruby upgrade, or c) provides an easy migration path.

What I'm asking

1. Is there any Ruby gem that:

accepts an HTML string and converts to PDF using a modern browser engine (Chrome) or otherwise supports flex/grid and modern CSS, and
is compatible with Ruby 2.5.1 / Rails 5.0.7.2?

1. If no gem fits, what are practical alternatives that integrate cleanly with a Rails 5 + Ruby 2.5 app and let me preserve my HTML templates? Examples I’m thinking of:

Running a small Node microservice (Puppeteer) that accepts HTML and returns PDF — examples or starter repos?
Using a 3rd-party API service (CloudConvert, HeadlessChromium.as-a-service, etc). Any recommendations for self-hosted / low-cost?
Strategies to safely upgrade Ruby to 2.7+ for this app (rough checklists, gotchas for Rails 5.0.7.2)?

1. If you’ve solved multi-page invoice layout issues with wkhtmltopdf, what CSS/practical fixes worked for you (page-break-* rules, avoiding table-cells across pages, float hacks)? I’ve tried:

page-break-inside: avoid on dynamic blocks
converting bottom two-column table into floating <div> columns with clear:both
limiting overflow-x and avoiding CSS grid/flex in PDF mode
but still got unpredictable full-column jumps when left column content is very large.

Appendix — key code snippets & errors

Controller (current):

def download_invoice
invoice = Invoice.find_by_id(params[:invoice_id])
pdf = generate_pdf(
@is_blur ? invoice.try(:invoice_html_blur, for_pdf: true) : invoice.try(:invoice_html, for_pdf: true)
)
send_data pdf, filename: "Invoice.pdf"
end

def generate_pdf(invoice_html)
WickedPdf.new.pdf_from_string(
invoice_html.encode('UTF-8', invalid: :replace, undef: :replace),
encoding: 'UTF-8',
footer: {
center: "Generated PDF",
right: "Page [page] of [topage]",
font_size: 8,
spacing: 2
},
dpi: 300
)
end

No
not really.
For Ruby 2.5.1 + Rails 5, you can use Wicked PDF, but modern flex/grid support will be unreliable. For proper modern CSS
you’d usually need Grover and therefore likely an upgrade to Ruby 2.7+

Thank you for this insightful discussion! Finding a reliable HTML→PDF gem that supports modern CSS is crucial as we adapt to contemporary web design standards. This topic opens up conversations about accessibility and user experience in digital documentation—truly vital in our increasingly visual world.