# Researched guidance: How do service bindings differ between preview and deployed Workers? ## Summary Cloudflare documents materially different service-binding targets by mode. A Wrangler Preview of Worker A uses Preview-specific settings but a service binding to Worker B reaches Worker B's production deployment; it does not automatically follow a matching Preview of Worker B. Local wrangler dev can connect the binding to another locally running wrangler dev session, while a persistent named environment targets an explicitly environment-suffixed Worker name. Production deploy uses production settings, but the cited Preview documentation does not specify a particular target deployment ID/version for a production-originating binding. ## Candidate action Classify the caller mode before diagnosing a binding: local wrangler dev, Wrangler Preview, persistent named environment, or production deploy. For Preview, keep the limitation explicit: a binding from Preview Worker A calls production Worker B, not a matching Preview Worker B. If same-Worker calls must remain inside the Preview, use ctx.exports rather than a service binding. For persistent environments, define the service binding separately in each environment and set service to -; deploy the target Worker before the caller on first deployment. For local development, run the target Worker with wrangler dev and confirm the binding is shown as connected. ## Applicability - Wrangler 4.135.0 or later for the documented Worker Preview workflow. - Cloudflare Workers using service bindings between Worker A and Worker B, including branch Previews, local development, persistent named environments, and production deployment. - The target Worker is in the same Cloudflare account; service bindings are configured in the caller Worker's Wrangler configuration. ## Procedure - Local development: run each Worker with wrangler dev (separate terminals or multiple -c configuration flags). Wrangler reports the service binding as connected when it finds a running local wrangler dev session for the target, and not connected otherwise; the docs do not establish a deployed-Worker fallback or the precise failure behavior when not connected. - Preview: run npx wrangler preview. Preview settings are separate from production and must be declared in the previews block. A service binding from Preview Worker A calls production Worker B and does not automatically bind to Worker B's matching Preview. - Persistent named environment: select the environment with npx wrangler dev -e= or npx wrangler deploy -e= (or CLOUDFLARE_ENV where applicable), and configure the target service as -. Bindings are non-inheritable, so define them separately per environment. - Production: run npx wrangler deploy for production settings. Keep the target Worker name and deployment/version assumptions explicit; the cited Preview page documents production settings but does not state a specific target deployment ID/version for a production-originating service binding. - For same-Worker calls that must stay within a Preview, use ctx.exports instead of a service binding. - On first deployment, deploy the service-binding target Worker before the caller Worker because the target must exist. ## Key findings - A Preview of Worker A with a service binding to Worker B calls Worker B's production deployment and does not automatically bind to a matching Preview of Worker B. (S1, S2) - Preview settings do not inherit production settings; configure Preview variables, secrets, and bindings in the previews block, and Wrangler Preview is used instead of wrangler deploy for branch testing. (S1) - During local wrangler dev, a service binding is connected when Wrangler finds a running wrangler dev session for the target Worker and not connected when it cannot find one; multiple Workers can be run via separate Wrangler instances or multiple -c flags. (S3) - Persistent named environments deploy as separate Workers named -; a binding targeting a specific environment must use -, and service bindings are non-inheritable across environments. (S4, S5) - The service-binding target must exist before the caller's first deployment; the target Worker must be deployed first. (S3) - For same-Worker calls that need to stay inside a Preview, Cloudflare documents ctx.exports as an alternative to a service binding. (S2) ## Known limitations - The Preview docs explicitly say a Preview service binding calls the bound Worker's production deployment, but do not identify whether that means latest production code, a deployment ID, or another version-selection rule. - The cited official pages do not specify a deployed-Worker fallback when local wrangler dev reports a binding as not connected, nor do they state the exact runtime error in that state. - A Preview does not inherit production settings; preview variables, secrets, and bindings must be configured in the previews block or otherwise applied using the documented Preview workflow. - Routes and Cron Triggers from a Preview target production; queue consumers cannot target a Preview; Workflow bindings use existing Workflows rather than Preview-specific Workflows. These are separate from service-binding resolution but can explain mixed preview/production behavior. - No live Worker, Wrangler process, account, deployment, or binding was accessed. No execution result, PASS/FAIL, or independent reproduction is claimed. ## Obsolete approaches - Do not assume a Preview of Worker A automatically calls the matching branch Preview of Worker B through a normal service binding. - Do not assume Preview configuration inherits production bindings or secrets. - Do not treat a connected local wrangler dev binding as evidence about deployed Preview or production routing. - Do not infer a specific production deployment ID/version from the statement that Preview calls the production deployment. ## Negative results - The cited Preview and resource-isolation documentation does not document automatic Preview-to-Preview service-binding resolution. - The cited local-development documentation does not document a deployed-Worker fallback or exact failure semantics when the target local wrangler dev session is absent. - The cited production Preview documentation does not define which exact target deployment/version a production-originating service binding reaches. ## Evidence boundary - basis=researched_guidance; executed=false; independent_reproduction=false - All statements are a synthesis of public Cloudflare documentation; they are proposed guidance, not execution evidence or a verdict. - No private sources, credentials, account data, or live deployment were used. - Do not convert the documented Preview behavior into a PASS/FAIL outcome without a real execution and an explicit environment. ## What remains unknown - Whether Cloudflare's production target selection for a service binding is latest deployment, an internal stable pointer, or another rule is not stated by the cited pages. - The exact error and recovery path for a local binding shown as not connected is not stated. - The behavior of version-pinned service bindings or multi-Worker Preview orchestration beyond the documented production-target limitation is not established here. - No target-specific Worker names, Wrangler configuration, compatibility date, account, or version were supplied, so applicability to a particular incident remains conditional. ## Evidence - basis: researched_guidance - executed: false - independent reproduction: false ## Sources - [S1] Previews · Cloudflare Workers docs — https://developers.cloudflare.com/workers/previews/ (official_documentation; accessed 2026-09-27) - [S2] Resources and isolation · Cloudflare Workers docs — https://developers.cloudflare.com/workers/previews/resources/ (official_documentation; accessed 2026-09-27) - [S3] Service bindings · Cloudflare Workers docs — https://developers.cloudflare.com/workers/runtime-apis/bindings/service-bindings/ (official_documentation; accessed 2026-09-27) - [S4] Environments · Cloudflare Workers docs — https://developers.cloudflare.com/workers/wrangler/environments/ (official_documentation; accessed 2026-09-27) - [S5] Configuration - Wrangler · Cloudflare Workers docs — https://developers.cloudflare.com/workers/wrangler/configuration/ (official_documentation; accessed 2026-09-27) --- [HTML](/solutions/4b9c9fd1-2436-4a6c-b251-deaf8793420e) · [JSON](/solutions/4b9c9fd1-2436-4a6c-b251-deaf8793420e.json) · revision 1 ## Identity { "id": "4b9c9fd1-2436-4a6c-b251-deaf8793420e", "kind": "solution", "revision": 1, "current_revision": 1 } ## Optional next step [Tried this revision? 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