Analyzer Architecture

FinFocus integrates with the Pulumi engine via the Pulumi Analyzer gRPC protocol, enabling zero-click cost estimation during pulumi preview and pulumi up. The analyzer intercepts resource definitions in real time, calculates projected costs through the normal plugin pipeline, and returns advisory diagnostics that Pulumi displays alongside its diff output.

Overview

The analyzer runs as a gRPC server that Pulumi launches as a subprocess. Pulumi sends individual resource definitions as they are evaluated, then sends the complete stack state once evaluation finishes. FinFocus returns cost diagnostics at both levels. Enforcement is always ADVISORY: diagnostics are informational and never block a deployment.

The implementation lives in internal/analyzer/ and is exposed through the finfocus analyzer serve CLI command (internal/cli/analyzer_serve.go).

Protocol

FinFocus implements the pulumirpc.AnalyzerServer interface from the Pulumi SDK (github.com/pulumi/pulumi/sdk/v3/proto/go). The server registers the following RPCs.

RPC	Purpose
Handshake	Completes the Pulumi analyzer handshake
ConfigureStack	Receives stack and project context; clears per-resource cost cache
Analyze	Receives a single resource; calculates and caches its projected cost
AnalyzeStack	Receives all resources; aggregates cached costs and emits summary diagnostics
GetAnalyzerInfo	Returns analyzer identity and active policy list
GetPluginInfo	Returns plugin version metadata
Cancel	Accepts a cancellation request (no-op; Pulumi always continues)

Note: Analyze is the per-resource RPC. AnalyzeStack fires once at the end of evaluation with the complete stack. Both are required by the protocol.

Port Handshake

The Pulumi Analyzer protocol requires a specific startup sequence.

1. finfocus analyzer serve binds a gRPC listener on a random TCP port.
2. It prints only the port number to stdout, for example 52341.
3. All log output goes to stderr exclusively.
4. Pulumi reads the port from stdout and connects.

This constraint means the analyzer command must not write anything else to stdout before or after printing the port, including log lines.

Interaction Sequence

sequenceDiagram
    participant P as Pulumi Engine
    participant A as finfocus analyzer serve
    participant E as Engine (cost pipeline)
    participant PL as Plugins (gRPC)

    P->>A: launch subprocess
    A-->>P: print port to stdout
    P->>A: Handshake()
    A-->>P: ack

    P->>A: ConfigureStack(stack, project)
    A->>A: clear per-resource cost cache
    A-->>P: ack

    loop for each resource in preview
        P->>A: Analyze(resource)
        A->>E: GetProjectedCost(ResourceDescriptor)
        E->>PL: gRPC GetProjectedCost
        PL-->>E: CostResponse
        E-->>A: CostResult
        A->>A: store result in per-resource cache
        A-->>P: []AnalyzeDiagnostic (per-resource cost)
    end

    P->>A: AnalyzeStack(allResources)
    A->>A: BuildCostSummary(cached results)
    A->>A: WriteCostSummary → last-cost-summary.json (atomic)
    A-->>P: []AnalyzeDiagnostic (stack summary + threshold)

    P->>A: Cancel() [optional]
    A-->>P: ack

Key Components

Server

Server in internal/analyzer/ implements pulumirpc.AnalyzerServer. It holds a reference to the FinFocus engine, a zerolog logger, and an in-memory map used to accumulate per-resource cost results between Analyze calls and the final AnalyzeStack call.

Resource Mapping

MapResource(res *pulumirpc.AnalyzerResource) engine.ResourceDescriptor converts a Pulumi resource representation into the internal format the engine accepts. MapResources applies the same transformation to a slice. The mapping extracts:

• Provider from the Pulumi type token prefix (e.g., aws from aws:ec2/instance:Instance)
• ResourceType as the full Pulumi type token
• SKU from resource inputs (instanceType, type, etc.)
• Region from resource inputs (availabilityZone, region)

Diagnostic Constructors

Function	Output
CostToDiagnostic(result)	Per-resource AnalyzeDiagnostic with projected monthly cost
StackSummaryDiagnostic(summary)	Aggregate stack-level cost summary diagnostic
WarningDiagnostic(message)	MEDIUM-severity warning for error conditions

All diagnostics carry EnforcementLevel = ADVISORY, which means Pulumi displays them but does not fail the operation.

Cost Aggregation

BuildCostSummary(results []CostResult) CostSummary aggregates the per-resource results accumulated during Analyze calls. It filters out failed results, detects mixed currencies, and produces a total. The summary is used by both StackSummaryDiagnostic and the threshold check.

WriteCostSummary(path string, summary CostSummary) error serializes the summary to last-cost-summary.json using an atomic write pattern (write to a temp file, then rename) to prevent partial reads.

The file is written under the Pulumi project’s .finfocus/ directory. Pulumi before 3.270.0 starts the analyzer in the project, so the analyzer finds the project itself. From 3.270.0 the analyzer runs in the policy pack directory, and the language host passes the project (RunPluginRequest.pwd) as FINFOCUS_PROJECT_DIR. Project-tier config and cost history use the same directory. An explicit FINFOCUS_PROJECT_DIR in the environment takes precedence.

Per-Resource Cache Lifecycle

The analyzer maintains an in-memory map of resource URN to CostResult.

• ConfigureStack clears the map, ensuring a fresh accumulation for each run.
• Analyze populates the map after calling the engine.
• AnalyzeStack reads the map, aggregates, and clears it.

This avoids re-querying plugins during AnalyzeStack for resources already priced during Analyze.

Cost Threshold Enforcement (v0.3.0)

When config.Analyzer.MaxMonthlyCost is greater than zero, AnalyzeStack emits an additional threshold diagnostic after the stack summary.

Condition	Severity	Meaning
Total cost <= threshold	MEDIUM	Stack is within the configured budget
Total cost > threshold	HIGH	Stack exceeds the configured budget

Both severities use EnforcementLevel = ADVISORY. The threshold diagnostic is skipped when:

• The result set contains mixed currencies.
• All resources failed cost calculation (no valid total is available).

The threshold is configured via config.yaml:

analyzer:
  max_monthly_cost: 500.00

Or via environment variable:

export FINFOCUS_MAX_MONTHLY_COST=500.00

Policy List

GetAnalyzerInfo returns the analyzer identity and its active policies. The policy list varies based on configuration.

Policy Name	Always Active	Condition
cost-estimate	Yes	Always returned
stack-cost-summary	Yes	Always returned
cost-threshold	No	Only when MaxMonthlyCost > 0

Graceful Shutdown

The server registers signal handlers for SIGINT and SIGTERM. On receipt, it closes cost plugin processes, including their process group on Linux and macOS, and then stops the gRPC server. It does not wait for Pulumi to hang up first: Pulumi waits for the analyzer process to exit, so that wait would never reach plugin cleanup. Pulumi treats a lost analyzer connection as non-fatal when the analyzer never served.

CLI Usage

# Start the analyzer server (Pulumi invokes this automatically)
finfocus analyzer serve

# Enable debug logging to stderr
finfocus analyzer serve --debug

Invoke the analyzer via the --policy-pack flag. The binary must be on your PATH:

export PATH="${HOME}/.finfocus/analyzer:${PATH}"
pulumi preview --policy-pack ~/.finfocus/analyzer

Pulumi 3.270.0 and later finds pulumi-language-finfocus on PATH and starts it as the language host. RunPlugin starts the analyzer in the policy pack directory, reads the port from its output, and connects over gRPC for the preview or update. Pulumi before 3.270.0 still starts pulumi-analyzer-policy-finfocus from PATH and reads the port the same way.

Note: Adding analyzers: to Pulumi.yaml does not work for YAML-runtime projects. Use --policy-pack with the binary on PATH.

Logging

All log output uses zerolog at the component level "analyzer". Logging goes exclusively to stderr. The port number printed to stdout must not be prefixed or suffixed with any other text.

Related Documentation

• System Overview - High-level architecture
• Cost Calculation - Engine calculation details
• Plugin Protocol - Plugin gRPC protocol
• CLI Reference - All CLI commands and flags