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Fix a failed Capistrano deployment by locating the first task that returned a non-zero status, then work outward from the failure boundary: SSH, server provisioning, Ruby and Bundler, Capistrano configuration, migrations, assets, secrets, or the application restart. Later errors are usually consequences of that first failure. A reliable recovery keeps the last published release serving traffic, corrects the smallest possible piece of shared state, and treats database changes separately from code rollback.
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Start with the first failed task
Capistrano executes tasks in order on one or more servers. When a task fails, later tasks are skipped or produce misleading follow-on errors. The useful error is therefore the first non-zero task, not the final line printed by the deploy command.
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- Run the deployment with tracing:
bundle exec cap production deploy --trace. - Capture the complete output, including the task name, host, command, exit status, and the first exception or operating-system error.
- If you need to inspect task ordering without changing the server, use the dry-run option supported by your Capistrano version:
bundle exec cap production deploy --dry-run. - Classify that first task before changing anything. An SSH task needs a different fix from
bundler:install,deploy:migrate, ordeploy:compile_assets.
Do not delete the current release, run a blind rollback, or retry repeatedly before identifying the boundary. Repeated attempts can make a transient lock, a partially written shared file, or a failed migration harder to diagnose.
Use the failure boundary to choose a safe fix
| First failing boundary | Typical symptoms | First checks | Reversibility and blast radius |
|---|---|---|---|
| SSH and host access | Authentication failed, connection refused, host-key warning, timeout, or permission denied before a remote command runs | Deployment user, host, port, private key, accepted host key, and authorized_keys |
Usually low blast radius; changing a key or firewall can affect every deployment host |
| Provisioning and SCM | ruby, git, database, or web-server command is missing |
Runtime versions, executable paths, package installation, and the server’s operating-system user | May affect other applications on the host; package and runtime changes should be planned |
| Dependencies | Bundler cannot resolve, compile, or install a locked gem | Ruby version, Bundler version, lockfile, native build tools, and persistent bundle configuration | Changing the lockfile changes the release; changing shared .bundle state affects subsequent releases |
| Capistrano or Rails integration | Unknown task, missing Rails task, or an option ignored | Capfile requires, plugin versions, and whether settings are in the correct file |
Configuration-only and generally reversible; affects all targets using that stage |
| Migration | deploy:migrate fails, database connection errors, lock timeouts, or incompatible schema errors |
Database credentials, rails_env, migration role and servers, and migration command |
Potentially high blast radius because schema changes persist and are not undone by code rollback |
| Assets | Compilation fails, a manifest is not found, or the release serves incomplete assets | Asset roles, prefix, manifest location, Node or asset-tool prerequisites, and writable release directories | Usually limited to the release, but a bad published manifest can affect all users immediately |
| Secrets and linked files | Missing encryption key, file-not-found, or permission denied while booting Rails |
Shared file existence, symlink target, owner, mode, and deployment-user read access | Shared-state change; correcting a secret path is reversible, replacing a production key may invalidate encrypted data |
| Restart and cutover | Deploy reports success but the old code continues serving, or the new process exits immediately | Process manager task, service name, release path, environment, and restart permissions | Can affect live traffic across all application servers; use one host or a maintenance strategy when possible |
Prove SSH access before debugging Rails
Capistrano’s own prerequisite is SSH. Rails, Bundler, migrations, and assets cannot be meaningfully diagnosed until the deployment user can open a non-interactive session to every target host. The installation guidance requires the deployment user’s public key to be present in ~/.ssh/authorized_keys on the destination server.
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Verify the exact connection Capistrano uses
- Read the stage file, commonly
config/deploy/production.rb, and record the server name, deployment user, port, and SSH options. Do not test with your personal account if Capistrano deploys as another user. - From the same machine that runs Capistrano, test the connection directly:
ssh -p 22 -i ~/.ssh/deploy_ed25519 deploy@example-host. Substitute the configured port, key, user, and host; do not assume port 22 or a default key. - For detail, add verbose SSH diagnostics:
ssh -vvv -p 22 -i ~/.ssh/deploy_ed25519 deploy@example-host. Look for which key is offered, whether the host key is accepted, and whether authentication falls back to a password prompt. - Run a non-interactive command such as
ssh -o BatchMode=yes deploy@example-host 'ruby -v'. A deployment must not depend on a hidden password, a shell prompt, or an interactive two-factor challenge.
Correct keys, host keys, and file permissions
- Install the public half of the deployment key in the destination user’s
~/.ssh/authorized_keys, not in the administrator’s account. Check that the file contains one complete key per line. - On the destination, the SSH directory and authorized-keys file must be owned by the deployment user and protected according to the SSH daemon’s accepted permissions. A directory or file writable by unrelated users can cause the daemon to reject it.
- Accept the host key deliberately on the machine that performs deployments. If a host was rebuilt and its key changed, verify the change out of band before removing the old entry from
known_hosts; do not disable host-key checking to hide the warning. - Confirm that the private key is readable by the account running the deploy and that an SSH agent is not being assumed unless your Capistrano configuration explicitly uses one.
- Check firewalls, security groups, DNS, and the configured port when the error is a timeout or connection refusal rather than an authentication failure.
When direct SSH works but Capistrano fails, compare the command’s user, key, port, host, and environment with the stage configuration. A shell alias or local SSH config used by your manual test may not be available to the Capistrano process.
Check provisioning and the source-control client
Capistrano transfers and orchestrates releases; it does not provision the application server. The project documentation states that Capistrano itself has no requirements beyond SSH, while an application commonly needs a database, a web server such as Apache or Nginx, and a language runtime such as Ruby.
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Confirm the deployment user’s runtime
After SSH succeeds, run these checks as the deployment user on each relevant host:
ruby -vandwhich rubyto verify the intended Ruby installation rather than a system Ruby or an interactive-shell shim.bundle -vandwhich bundleto verify Bundler is installed for that Ruby.git --versionandwhich gitif the configured SCM is Git.- The database client or socket required by the application, plus connectivity to the configured database endpoint.
- The web server and process manager expected to serve the release, including service names and restart permissions.
Non-login SSH shells often load fewer profile files than an interactive terminal. If Ruby is installed by a version manager, configure Capistrano’s command environment or PATH explicitly rather than relying on a developer’s shell initialization.
Check SCM access separately
A deployment can authenticate to the application server and still fail when that server fetches the repository. Confirm the repository URL, the server-side deploy key or token, outbound network access, and the presence of the SCM binary. Test a read-only fetch as the same operating-system user and use the exact repository revision referenced by the deploy. A repository permission failure is not fixed by changing the application server’s SSH key unless that key is also the credential used for SCM access.
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Make Ruby, Gemfile, and Bundler agree
Once the server and repository are reachable, dependency installation is the next common boundary. The deployed Ruby must satisfy the Gemfile’s Ruby requirement, and Bundler must be able to install the versions recorded in Gemfile.lock. Native extensions additionally require the operating-system headers and compilers expected by those gems.
Read the dependency error, not just the final exit code
- An error saying the current Ruby is outside the Gemfile requirement means the runtime must be changed or the application must be intentionally updated; installing a different Bundler alone will not solve it.
- A lockfile-platform error means the lockfile does not include the platform used by the server. Resolve it in development with the project’s supported Bundler workflow, review the resulting lockfile change, and deploy that change deliberately.
- A compiler or header error identifies a missing system package for a native gem. Install the package through the host’s provisioning process rather than modifying the application bundle ad hoc during a deploy.
- Permission errors under the bundle path indicate ownership or a read-only filesystem, not a Ruby dependency conflict.
Run and persist the Bundler task
Capistrano Rails exposes the Bundler task, which can be isolated from the rest of a deployment:
bundle exec cap production bundler:install
Use that command after correcting the runtime or host package issue. If your deployment relies on a persistent bundle configuration, keep the bundle directory across releases:
append :linked_dirs, ".bundle"The shared .bundle directory affects repeatability: it can preserve deployment-specific settings, but stale settings can also keep reproducing a bad path or excluded group. Inspect the shared configuration when behavior differs between a fresh host and an established host. Keep development and test groups excluded only when that matches the application’s production needs, and ensure the same policy is represented in your Capistrano settings and lockfile workflow.
Repair the Capistrano and Rails integration
The Rails tasks for migrations and asset compilation come from the Capistrano Rails integration. If a task is unknown or silently absent, first check that the integration is loaded and that its version matches the Capistrano version in the bundle.
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Put requires in the Capfile
The Rails integration documentation specifically says that require statements belong in Capfile, not in config/deploy.rb. A minimal Capfile for a Git-backed Rails deployment commonly includes:
require "capistrano/setup"
require "capistrano/deploy"
require "capistrano/rails"Some applications load the Bundler, asset, and migration components explicitly instead of loading the combined Rails integration. Use one consistent approach, keep all requires in Capfile, and commit the file with the application. Do not hide task loading in a stage file where it can differ between environments.
Check stage and role definitions
Confirm that the production stage defines the roles expected by the Rails tasks, such as :app, :web, and :db. A migration or asset task can fail simply because no server is assigned the role it is configured to use. Compare the stage’s roles with the actual topology before changing task code.
Fix migration failures without guessing
Capistrano Rails supplies cap production deploy:migrate and defaults the migration command to db:migrate. The integration also exposes settings for the Rails environment, migration role, migration servers, and migration command. Those settings must describe the servers that can reach the production database.
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rails_envmust be the environment whose credentials and database configuration are intended for this release, normallyproduction.migration_rolemust name a role assigned to a host with database access. If the role is:dbbut no server has that role, the task has nowhere to run.migration_serversmust select the correct host or primary host in a multi-server deployment. Do not run the same migration concurrently on every application server unless the topology and database locking strategy explicitly support it.migration_commandshould remaindb:migrateunless the application intentionally uses another Rails task.
After a connection error, test the database endpoint, credentials, TLS requirements, and firewall from the selected migration host as the deployment user. After a lock timeout, inspect another migration process and the database’s active locks rather than launching parallel retries.
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Handle schema compatibility as a separate decision
A migration that ran successfully can still leave old application processes unable to read the schema, or a new release can expect a column before every process has been restarted. Use an expand-and-contract approach for changes that must coexist across releases: add compatible structures first, deploy code that can use both forms, backfill safely, and remove obsolete structures only after the old code is gone. Never assume that deploy:rollback will reverse a migration; Capistrano rollback changes the release selection, not the database schema.
Resolve asset compilation and manifest problems
Asset failures usually come from a mismatch between the Rails application’s asset layout and Capistrano’s asset settings. Check assets_roles, assets_prefix, and assets_manifests against the application rather than copying values from another project.
Check roles and paths
assets_rolesmust include the hosts that have the Ruby, Node, and asset-tool prerequisites and are intended to compile assets.assets_prefixmust match the URL and directory prefix configured by the Rails application. A prefix mismatch can publish files in a directory the web server never serves.assets_manifestsmust identify the manifest produced by the installed Rails asset pipeline. Rails versions and asset systems use different manifest names and locations; inspect the release’s actualpublictree instead of assuming one path.
Run the task directly to separate compilation from the rest of the deploy: bundle exec cap production deploy:compile_assets. Check the first compiler error for missing Node packages, unsupported Ruby or JavaScript versions, filesystem permissions, or an application initializer that cannot boot without a secret. If compilation succeeds but browsers receive old or missing files, compare the generated manifest, the configured prefix, and the web server’s document root for the newly published release.
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Repair linked secrets and file permissions
Production secrets should live in shared storage and be linked into each release. A Rails application that uses encrypted credentials commonly requires config/master.key at boot. The file must exist on the server before the release starts and must be readable by the deployment or application user that loads Rails.
Configure the shared file
set :linked_files, fetch(:linked_files, []).push("config/master.key")Create the corresponding file under the application’s shared directory through your secret-management procedure, not by committing it to the repository. The path, owner, and mode must allow the process that boots Rails to read it while preventing unrelated users from reading it.
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Diagnose a missing or unreadable key
- Inspect the failed release’s symlink and resolve its target into the shared directory.
- Confirm that the target exists on every host that can run Rails or restart the application.
- Check ownership and mode as the deployment user, then test read access without printing the key:
test -r /path/to/shared/config/master.key. - Verify that the application server’s runtime user, which may differ from the deployment user, can read the linked file.
- Redeploy or restart only after the shared file is correct; changing the key itself can make existing encrypted data unreadable.
A permission-denied message for a secret is distinct from a missing-file message. Fix the specific owner, group, directory traversal permission, or security-policy rule rather than making the secret world-readable.
Make the restart task match the process manager
Capistrano can publish release files, but it cannot infer whether the application uses Puma, Passenger, Foreman, systemd, or another process manager. A deployment can therefore finish while an old process continues serving the previous release.
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Use the process manager’s documented reload or restart operation and attach it to the publish point. For a systemd-managed service, the shape of a task might be:
namespace :deploy do
task :restart do
on roles(:app) do
execute :sudo, :systemctl, :restart, "myapp"
end
end
end
after "deploy:published", "deploy:restart"Replace the service name, privilege method, and role with values from your host. If passwordless sudo is not configured for the deployment user, this task will fail by design; configure a narrowly scoped policy or use the process manager’s approved deployment interface. Test the task on one non-critical host, verify the new process’s release path and environment, then check application health before restarting the remaining servers.
Distinguish a restart failure from a bad release
- If the service never receives a restart command, the Capistrano hook or role selection is wrong.
- If the command runs but the old code remains, inspect the service’s working directory, workers, and reload semantics.
- If the new process exits, read the process manager’s logs for missing secrets, incompatible dependencies, bind errors, or database connectivity.
- If only some servers change, compare roles, host lists, and service status across the fleet.
Recover safely after a failed deployment
When a task fails before final cutover, the previously published application generally continues serving traffic. Capistrano closes outstanding SSH work on other servers after a non-zero task result, but you should still inspect each host for the release directory, process state, and any command that may have completed before the failure.
Choose between fixing forward and rolling back
| Situation | Preferred action | Why |
|---|---|---|
| Failure during SSH, provisioning, dependency installation, or an unpublished release | Correct the host or configuration issue and redeploy | The previous published release remains the safer serving version; no release selection change is needed |
| Code is wrong but the database schema remains compatible | Revert the bad commit and deploy the corrected code | Capistrano documentation says reverting and redeploying is preferable in many failed-deployment situations |
| Code is published and application health is failing, with a schema that supports the previous release | Use the tested release rollback procedure, then investigate | Restores a known release, but does not undo database changes |
| Migration changed or removed data structures | Stop and use a database-aware recovery plan | Release rollback alone cannot reverse migrations and may make the old code incompatible |
| Only one host is unhealthy in a multi-server fleet | Remove that host from traffic, repair or redeploy it, then restore it after health checks | Limits blast radius while preserving healthy capacity |
Before an incident, test the exact rollback and redeploy procedures in an environment that mirrors production. Record which commands change release symlinks, which commands restart services, how database backups are restored, and who can execute each step. A rollback that exists only as an untested command is not a recovery plan.
Prevent the next Capistrano failure
- Run the same Ruby and Bundler versions in CI and on the deployment host, and fail early when the Gemfile’s Ruby requirement is not met.
- Keep
Capfilerequires under version control and review stage roles whenever the server topology changes. - Provision Ruby, Git, database access, the web server, asset prerequisites, service units, firewall rules, and deployment-user permissions separately from application deployment.
- Store secrets in shared files or an approved secret system, verify their presence on every target host, and never commit
config/master.key. - Persist only the shared directories that the application needs, including
.bundlewhen the deployment relies on it, and review shared state after runtime or Bundler changes. - Make migrations backward-compatible with the code currently serving traffic and document the migration owner and server selection.
- Attach an explicit restart task to the publish lifecycle and verify the running process’s release path after every production deploy.
- Keep a runbook containing the first-failure triage command, direct SSH test, host inventory, secret locations, migration procedure, health checks, and tested recovery steps.
The durable troubleshooting order is intentional: establish SSH, verify the provisioned host, make Ruby and Bundler deterministic, load the Rails tasks correctly, then inspect migrations, assets, secrets, and restart behavior. That sequence prevents a downstream Rails symptom from hiding the infrastructure or configuration error that caused the deployment to stop.
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