Replace pygal with matplotlib for chart rendering - #2150
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Removes the last LGPL-3.0 dependency in the runner, following the same path #2136 took for fpdf2 -> reportlab and CairoSVG -> resvg. matplotlib is a free swap: prometheus-api-client already requires it, so all ten packages in its tree were installed in the image before this change. The lock diff is two removals (pygal and its importlib-metadata pin) and no additions. New robusta.core.reporting.charts provides XYChart, BarChart and TreemapChart behind the same add()/render() surface the chart builders and playbooks were written against, so GraphBlock, add_pngs_for_all_svgs and every sink are untouched - render() still returns SVG bytes at a fixed pixel size. Implementation notes: - driven through matplotlib's Figure/FigureCanvasSVG API rather than pyplot, so there is no global figure registry to leak and no backend to select - text is emitted as paths, so resvg rasterizes correctly with no fonts installed in the container - the root <svg> width/height are rewritten to exact pixels, because matplotlib emits points and the sinks rely on a known raster size - svg.hashsalt is pinned, so identical input renders to identical bytes instead of picking up a fresh uuid per render - MPLBACKEND=Agg is set in the image; Robusta never selects a backend, but a transitive pyplot import would otherwise probe for a GUI toolkit - treemaps use a squarified layout and caption tiles in place, which pygal could not do - charts_style() keeps its name and signature (it is exported through robusta.api) and now returns a ChartStyle; the PlotCustomCSS temp-file hack it needed for pygal is deleted Validation: 25 new tests cover SVG output and exact raster size, deterministic bytes, legend truncation, dashed strokes, empty and all-zero data, the bar chart's missing-value sentinel, and four properties of the squarified layout. The suite's failure set is byte-for-byte identical to the base branch. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LrHLcp11gc2cJoWtA9C7kA
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✅ Docker image ready for
Use this tag to pull the image for testing. 📋 Copy commandsgcloud auth configure-docker us-central1-docker.pkg.dev
docker pull us-central1-docker.pkg.dev/robusta-development/temporary-builds/robusta-runner:e83a1df
docker tag us-central1-docker.pkg.dev/robusta-development/temporary-builds/robusta-runner:e83a1df me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:e83a1df
docker push me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:e83a1dfPatch Helm values in one line: helm upgrade --install robusta robusta/robusta \
--reuse-values \
--set runner.image=me-west1-docker.pkg.dev/robusta-development/development/robusta-runner-dev:e83a1df |
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Pro Run ID: 📒 Files selected for processing (2)
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Included review availability: 1 review is currently available. Based on recent review activity, included reviews refill at 4 per hour. WalkthroughThe PR replaces Pygal with matplotlib-backed chart classes. It adds line, bar, and treemap rendering, updates Prometheus and node CPU integrations, configures headless rendering, and updates chart and SVG conversion tests. ChangesChart rendering migration
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The chart-rendering backend replacement is merge-ready after normal checks and review; no actionable merge-blocking risk remains. Sequence Diagram(s)sequenceDiagram
participant Prometheus
participant PrometheusEnrichmentUtils
participant XYChart
participant SVGConversion
Prometheus->>PrometheusEnrichmentUtils: provide query results
PrometheusEnrichmentUtils->>XYChart: build chart and add series
XYChart-->>SVGConversion: return SVG output
SVGConversion-->>PrometheusEnrichmentUtils: convert SVG for downstream formats
Possibly related PRs
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
Comment |
Set MPLBACKEND to Agg to prevent GUI toolkit probing.
Running all 22 chart-producing and chart-consuming paths end to end surfaced three defects that the unit tests missed: - A query returning no series fell back to a placeholder x-range of (0, 1), so every x tick rendered as "Jan 1 00:00". pygal drew no x-axis at all in this case, making this a regression. The axis is now left unlabelled when there is no data. - A single-sample query gives a zero-width x-range, and matplotlib emitted "UserWarning: Attempting to set identical low and high xlims" on every such chart. The limits are now widened explicitly rather than relying on the auto-expand. - With a single sample and show_dots=False - which is how the alert pipeline builds every series - there is no segment to draw, so the chart came out blank. pygal behaved the same way, so this is not a regression, but a chart that plots valid data as nothing is not working. A marker is forced when a series has exactly one point. Each fix has a regression test; test_charts.py is now 28 tests. The suite's failure set remains byte-for-byte identical to the base branch. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LrHLcp11gc2cJoWtA9C7kA
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Inline comments:
In `@src/robusta/core/reporting/charts.py`:
- Around line 262-263: Update the y-axis limit handling around chart.range so
equal bounds, including (0, 0), are expanded to a non-degenerate range before
calling ax.set_ylim. Preserve the existing range behavior for unequal bounds.
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Fix all unresolved CodeRabbit comments on this PR:
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Addresses CodeRabbit's review finding on PR #2150. Both chart builders derive the y-range from the maximum sample, so a metric that is flat at zero - an error-rate counter with no errors, for example - collapses chart.range to (0, 0). That tuple is still truthy, so ax.set_ylim(0, 0) was called and matplotlib warned about a singular transform before picking its own bounds. This is the y-axis twin of the zero-width x-range already handled a commit earlier; the guard was asymmetric. Equal bounds now get height explicitly. The same collapse also makes every derived y tick identical - the range/4 interval is zero, so y_labels comes through as [0, 0, 0, 0, 0] and five labels were drawn on top of each other. Duplicate ticks now collapse to one. Also documents _worst_ratio, the squarify aspect-ratio heuristic, which was the one genuinely non-obvious function without a docstring. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LrHLcp11gc2cJoWtA9C7kA
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Summary
This PR replaces pygal with matplotlib as the chart rendering backend for Robusta's Prometheus/resource graphs. The new implementation uses matplotlib's object-oriented API to generate SVG charts that are rasterized for chat platforms that don't support SVG.
Key Changes
New chart module (
src/robusta/core/reporting/charts.py):XYChart,BarChart, andTreemapChartclasses with a pygal-compatible surface (add()+render()methods)Figure/FigureCanvasSVGAPI for deterministic, stateless renderingChartStyledataclass replacing pygal'sStylewith the same visual configurationUpdated dependencies:
pygaldependencymatplotlibas primary chart rendererpyproject.tomlandDockerfileto reflect new dependenciesRefactored chart building:
prometheus_enrichment_utils.py: Updated to useXYChartinstead ofpygal.Graphnode_cpu_analysis.py: Updated to useBarChartandTreemapChartfrom new modulecustom_rendering.py: Simplifiedcharts_style()to returnChartStyleinstead of pygalStyle; removedPlotCustomCSSclassAPI exports (
src/robusta/api/__init__.py):XYChart,BarChart,TreemapChart, andChartStylefor playbook useComprehensive test coverage (
tests/test_charts.py):Implementation Details
width/heightattributes to exact pixel valuesadd()andrender()interface that playbooks were written againsthttps://claude.ai/code/session_01LrHLcp11gc2cJoWtA9C7kA