Modular vs Monolithic: How Apps Choose Their Own Execution

Modular vs Monolithic: How Apps Choose Their Own Execution (App-Chains, RaaS, and Rollups)

In 2025, teams must decide: ship on a shared monolith (single chain with execution+consensus+data) or compose a modular stack (rollup with outsourced data availability, shared settlement, optional custom sequencers). This guide lays out a builder’s decision tree covering costs, latency, MEV, and operational risk with practical checklists and links to the best references.

Read alongside the canonical docs for Ethereum rollups, OP Stack, Arbitrum, Polygon CDK, Celestia DA, EigenLayer/EigenDA, Cosmos SDK, Avalanche Subnets, and Solana.

TL;DR (founders & PMs):
  • Monolithic chains (execution+consensus+DA on one chain) deliver simplicity and liquidity concentration. Example references: Solana cluster, base L1s like Ethereum L1 (though it now favors modular scaling via rollups).
  • Modular stacks decompose execution, DA, and settlement. Builders choose: settlement (Ethereum/L1), DA (Ethereum, Celestia, EigenDA), proving (ZK/Optimistic), and sequencers (shared/decentralized/based). You can rent this via rollups-as-a-service (RaaS) like Conduit, Caldera, AltLayer, Gelato, Zeeve.
  • Decision rule of thumb: If your app needs hard real-time UX, custom fees/MEV policy, and predictable blockspace, a modular app-chain/rollup is compelling. If you want instant access to users/liquidity, shared monolithic blockspace may win.
  • Costs: Rollup total cost = prover cost + DA cost + sequencer infra + L1 settlement fees. On monoliths, you “pay with congestion risk” but offload infra.
  • Latency & MEV: ZK rollups have faster finality than optimistic (no 7-day challenge by default), but proving overhead matters. MEV policy is configurable on your own chain; shared chains inherit ecosystem MEV/PBS rules. See PBS, Flashbots, and Arbitrum MEV.

Primer: monolithic vs modular (and why it matters)

Monolithic architecture means one chain handles execution, consensus, and data availability in one place. Historically, this maximizes developer simplicity and composability but risks congestion every dApp competes for the same blockspace. References: Solana cluster model, Ethereum’s scaling journey.

Modular architecture decomposes the stack: an app executes on its own rollup or app-chain, posts data to a separate DA layer (Ethereum, Celestia, EigenDA), and settles to a chosen settlement layer (often Ethereum). You can add custom sequencers and choose ZK vs optimistic proving. References: Celestia, EigenLayer, Rollups.

Why the choice is hot in 2025:
  • Traffic spikes & celebrity apps can degrade shared UX; teams want predictable lanes.
  • Cost visibility: rollups now expose line-items (DA, proofs, sequencers) you can optimize.
  • MEV policy: apps want control over orderflow, privacy, and cross-domain MEV leakage.

Decision diagram: which path should you take?

Intent → Constraints → Recommendation
Intent
  • High-volume micro-tx
  • Low tail latency
  • Custom fees/MEV
  • Predictable blockspace
Constraints
  • Budget for prover/DA?
  • Compliance routing?
  • Liquidity access needs?
  • Team ops maturity?
Recommendation
  • Yes to all → Modular app-rollup
  • Budget tight or compo critical → Shared L2
  • Zero-ops, fastest launch → Monolithic with great wallet UX
Short rule: If you must control ordering/fees and guarantee throughput for an app class (DEX, real-time game, social feed), you’ll likely end up modular. If most value comes from composability with big DeFi/NFT pools, stay on a shared chain.

Cost model: what you actually pay (with knobs you can turn)

For modular rollups, total cost typically breaks down into:

  1. DA cost: bytes posted to DA layer (Ethereum blob/4844 markets), or external DA like Celestia / EigenDA.
  2. Proof cost: ZK proving (hardware or cloud) or challenge infra for optimistic.
  3. Sequencer: hosting, HA, monitoring; decentralized/shared options may carry fees.
  4. Settlement: posting state roots to L1, finalization gas, bridge maintenance.
  5. RaaS margin: if using Conduit/Caldera/AltLayer/Gelato/Zeeve, you pay a platform fee for SLA and ops.
// Pseudocode: monthly rollup budget rougher const tx = 20_000_000; // monthly tx count const bytesPerTx = 500; // avg compressed bytes posted to DA const daPricePerMB = 0.50; // example blended blob/DA rate (check live markets) const proofCostPerTx = 0.00001; // ZK amortized in $ const seqInfra = 6000; // HA infra + ops const raasFee = 8000; // platform + support const daMB = (tx * bytesPerTx) / 1_000_000; const daCost = daMB * daPricePerMB; const proofCost = tx * proofCostPerTx; const total = daCost + proofCost + seqInfra + raasFee; console.log({ daMB, daCost, proofCost, total });

Monolithic chains externalize these costs into on-chain fees; your app pays per tx and absorbs congestion risk. If your spikes are rare and your UX tolerates occasional delay, monolithic can be cheaper overall. If you run consistent high load, modular gives you predictable spend and priority control.

Cost component Monolithic chain Modular (rollup/app-chain) Knobs
Execution Per-tx gas; shared mempool Sequencer infra + priority rules Block time, gas target, fee policy
Data Availability Baked into gas model Ethereum blobs / Celestia / EigenDA Compress, batch, choose DA market
Proofs N/A ZK prover cost or optimistic monitoring ZK flavor, recursion, proving hardware
Ops Wallet support, RPC quota Sequencer HA, bridge, monitoring RaaS vendor, SLOs, runbooks

Latency & finality: UX differences users actually feel

Latency is the time to see an accepted transaction; finality is when it’s economically infeasible to revert. On modular stacks:

  • Optimistic rollups achieve fast local confirmation but rely on a challenge window (e.g., ~7 days on Ethereum) for economic finality. See optimistic rollups.
  • ZK rollups post succinct proofs to L1; users get strong finality once proofs are accepted. See Polygon zkEVM, Scroll, zkSync, Starknet.
  • Shared L2s (OP Mainnet, Arbitrum, Base) provide battle-tested infra and strong wallet support with good enough UX for most apps.
  • Monolithic chains like Solana focus on single-state high throughput with local fee markets and QUIC to lower tail latency.
Rule of thumb: If your UX needs near-instant economic finality (large trades, high-stakes in-game assets), ZK rollups or monolithic chains shine. If you can tolerate bounded reorg risk with strong UX, optimistic is often cheaper today.

MEV & sequencers: who orders your transactions (and at what price)?

MEV (maximal extractable value) emerges when transaction order affects value. Policy depends on stack:

  • Shared chains inherit ecosystem-level MEV norms: Flashbots on Ethereum, PBS research, Arbitrum MEV policies.
  • App rollups can implement:
    • Centralized sequencer (fastest iteration, single operator risk).
    • Shared/decentralized sequencers (e.g., research ecosystem, community efforts).
    • Based sequencing integrated with L1 proposers (see based rollups concept).
  • Orderflow policy: you decide auction design, private tx lanes, back-run rebates, or privacy relays.
Practical MEV mitigations:
  1. Adopt private mempool or encrypted orderflow for sensitive tx.
  2. Expose a request-for-quote path for retail swaps to reduce slippage.
  3. Share back-run rebates with users/LPs via your auction policy.
Further reading: Flashbots, ethresear.ch, Arbitrum MEV.

Rollups-as-a-Service (RaaS): renting your stack with SLAs

RaaS providers host and operate your rollup sequencers, DA plumbing, bridges, monitoring so you can ship in weeks. Leading platforms:

  • Conduit (OP Stack, Base-class chains; blob usage dashboards).
  • Caldera (OP/Arbitrum stacks; integrated oracles, indexers).
  • AltLayer (restaked rollups, ephemeral rollups for events).
  • Gelato RaaS (automation + rollups).
  • Zeeve (multi-stack enterprise focus).
  • Polygon CDK (ZK chain kits with shared liquidity designs).
  • Arbitrum Orbit (app-specific L3s anchored to Arbitrum).
Vendor due-diligence checklist:
  1. Uptime SLO for sequencers/bridges; incident history and public postmortems.
  2. DA options (Ethereum blobs, Celestia, EigenDA) and migration plan.
  3. ZK/optimistic flavors supported; proof recursion and cost model.
  4. Exit safety: what happens if the vendor disappears?
  5. Monitoring & analytics: blobs usage, proof costs, latency p50/p95, MEV telemetry.

Comparing popular stacks (practical fit)

Stack Type DA / Settlement Latency/Finality Best for Docs
OP Stack / Base-class L2 Optimistic rollup Ethereum blobs / Ethereum settlement Fast local confirm; 7-day challenge General consumer, low ops Optimism / Base
Arbitrum Orbit Optimistic L3/L2 Arbitrum / Ethereum Good UX; challenge window Games/DEX with close Arbitrum ties Docs
Polygon CDK / zkEVM ZK rollup or validium config Ethereum; optional alt-DA Stronger finality; prover cost Gaming, marketplaces needing ZK guarantees Docs
Cosmos SDK + IBC Sovereign app-chain Own validators; ICS for shared security Configurable; ops heavy High-customization, IBC native Docs
Avalanche Subnet App-chain (custom VM) Own validators; Subnet fees Low latency; tuned economics Games/DeFi with custom logic Docs

Playbooks: concrete paths with trade-offs

Playbook A — Stay on a shared L2 (fastest to users)

  • Launch on Base / OP Mainnet / Arbitrum.
  • Rely on wallets, infra, fiat on-ramps already present.
  • Optimize gas with batching & calldata compression; consider account abstraction (AA) where supported.
  • Accept MEV norms; add private tx lanes for sensitive flows.

Playbook B — Launch your own rollup (predictable blockspace)

  • Pick stack: OP Stack (optimistic) or Polygon CDK/zkEVM/Scroll/Starknet (ZK).
  • Choose DA: Ethereum blobs for alignment, or Celestia/EigenDA for cost/throughput mix.
  • Start with centralized sequencer; roadmap to decentralized/shared.
  • Instrument KPIs: p50/p95 latency, failure rate, DA $/MB, prover $/tx, bridge TVL, MEV revenue sharing.

Playbook C — Sovereign app-chain (max control)

  • Use Cosmos SDK or Avalanche Subnets for bespoke logic and fees.
  • Plan validator set, bootstrap incentives, and IBC/bridge strategy.
  • Budget significant ops and governance overhead; consider shared security via Cosmos ICS.
Common failure modes:
  • Liquidity isolation: launching a chain without strong bridge/liquidity plans.
  • Ops surprises: underestimating prover/DA bills or sequencer HA needs.
  • Governance deadlock: MEV policy and upgrade keys unclear; slows shipping.

Case studies & patterns

dYdX → app-chain (Cosmos)

dYdX moved from an Ethereum-based model to a Cosmos app-chain to control orderflow and latency for a high-throughput orderbook DEX. Result: bespoke match logic, fee policy, and validator incentives. Trade-off: liquidity fragmentation and higher ops. Reference: docs.

Immutable zkEVM (Polygon CDK) for gaming

Immutable uses Polygon’s ZK stack to deliver game-ready throughput with Ethereum alignment and shared liquidity bridges. Developers get L2-like UX with gaming-friendly primitives. Reference: announcement, CDK.

Base (OP Stack) for consumer apps

Base leverages the OP Stack and Coinbase distribution. For consumer apps prioritizing wallets, on-ramps, and partnerships, piggybacking on a strong shared L2 often beats going sovereign early. References: docs, OP Stack.

Arbitrum Orbit L3s for games/DEXs

Orbit enables app-specific chains inheriting Arbitrum tech, giving predictable blockspace while retaining Arbitrum proximity. Good fit when you need special gas/MEV policy but want Arbitrum bridges and tooling.

Avalanche Subnets for custom economics

Projects needing bespoke fee tokens or VM logic choose Subnets, often for real-time games. You control validator sets and economics, at the cost of more ops and liquidity planning.

FAQ

Is modular always cheaper at scale?

Not always. Rollups expose DA/prover costs you can optimize, but you also pay sequencer/ops and RaaS margins. If your load is spiky and you don’t need control, a shared L2 can be cheaper. Check blob markets (EIP-4844), DA vendors (Celestia/EigenDA), and expected tx profile.

What do I lose leaving a shared L2?

Composability and immediate liquidity. You must build/bridge liquidity, incentivize market makers, and maintain wallet/RPC support. Many successful app-chains had a pre-existing userbase, strong incentives, or a killer feature (e.g., orderbook control).

ZK or optimistic?

ZK offers stronger finality and often better cross-domain security assumptions; optimistic is simpler/cheaper today and battle-tested. Your choice hinges on UX tolerance, budget, and partner stack availability.

Can I start on a shared L2 and migrate later?

Yes. Design with migration hooks: abstract RPC endpoints, keep addresses upgradeable (proxy patterns on EVM), and prepare a state snapshot + token bridge plan. Several teams start on Base/OP/Arbitrum, then graduate to app-rollups via RaaS.

References & further reading

© TokenToolHub — Practical architecture guides for Web3 builders. Validate assumptions against the live docs and pricing pages linked above; DA/proving/fee markets change frequently.