Limits
Last updated August 23, 2023
This article is an aggregation of the limits imposed on various components of the Heroku platform.
Limits exist for several reasons. Some exist because of the architecture of the Heroku platform (for example, Heroku stores only the most recent 1500 lines of an app’s log history). Others exist to ensure good platform citizenship (for example, you can’t make more than 4500 Platform API requests per hour).
Many of the limits listed below link to another Dev Center article that provides additional context regarding the limit.
Apps
App names
App names cannot exceed 30 characters.
Maximum number of apps
An account can have no more than 100 apps.
Maximum custom domains per app
A single app can have up to 1,000 custom domains assigned to it.
Logs
Log history
Heroku only stores the last 1500 lines of log history. If you’d like to persist more than 1500 lines, use a logging add-on or create your own syslog drain.
Drains
You can have up to 5 drains on any given app.
Line length
Lines generated by dynos that exceed 10000 bytes are split into 10000 byte chunks without extra trailing newlines. Each chunk is submitted as a separate log line.
Build, CI and Release Phase
Log output generated by builds, CI runs and release phase are limited to 300 MB. Any output reaching that limit will be truncated from its beginning in chunks of 150 MB.
Router
HTTP timeouts
HTTP requests have an initial 30 second window in which the web process must return response data (either the completed response or some amount of response data to indicate that the process is active). Processes that do not send response data within the initial 30-second window will see an H12 error in their logs.
After the initial response, each byte sent from the server restarts a rolling 55 second window. A similar 55 second window is restarted for every byte sent from the client.
If no data is received from the dyno within the 55 second window the connection is terminated and an H15 error is logged.
Similarly, if no data is received from the client within the 55 second window, the connection is terminated and an H28 error is logged.
HTTP response buffering
The router maintains a 1MB buffer for responses from the dyno per connection.
HTTP request buffering
When processing an incoming request, a router sets up an 8 KB receive buffer and begins reading the HTTP request line and request headers. Each of these can be at most 8 KB in length, but together can be more than 8 KB in total. Requests containing a request line or header line longer than 8KB will be dropped by the router without being dispatched.
Dynos
Dyno memory
Different dyno sizes offer different amounts of maximum RAM:
eco,basic, andstandard-1xhave 512 MBstandard-2xhas 1024 MBperformance-mhas 2.5 GBperformance-lhas 14 GB
Dyno memory and restarts
If the memory size of your dyno keeps growing until it reaches two times its quota (for a standard-1x dyno, 512 MB x 2 = 1 GB), the dyno manager will restart your dyno with an R15 error.
Attached one-off dyno timeout
Connections to one-off dynos will be closed after one hour of inactivity (in both input and output). When the connection is closed, the dyno will be sent SIGHUP. This idle timeout helps prevent unintended charges from leaving interactive console sessions open and unused.
Detached one-off dyno timeout
Detached one-off dynos are cycled every 24 hours. As a result, a one-off dyno will run for a maximum of 24 hours
Concurrent one-off dynos
The following limits exist per app:
- 1
ecoone-off dyno - Up to 50 concurrent one-off
basicdynos - Up to 50 concurrent one-off
standard-1xdynos - Up to 50 concurrent one-off
standard-2xdynos - Up to 5 concurrent one-off
performance-mdynos - Up to 5 concurrent one-off
performance-ldynos
Submit a request to raise this limit for your application.
Config vars
Config var data (the collection of all keys and values) is limited to 32kb for each app.
Boot timeout
The web process in a dyno may not take more than 60 seconds to bind to its assigned $PORT.
If your application requires more time to boot, you may use the boot timeout tool to increase the limit. However, in general, slow boot times will make it harder to deploy your application and will make recovery from dyno failures slower, so this should be considered a temporary solution.
Exit timeout
When a dyno is killed or restarted, the processes within the dyno have 30 seconds in which to exit on receiving a SIGTERM. The process is sent SIGKILL to force an exit after this 30 seconds.
Dyno restart limits
These limits are documented in Automatic dyno restarts and Dyno crash restart policy.
Dyno scale
The eco and basic dyno types support a maximum of one running dyno per process type. Additionally, applications that use the eco dyno type are limited to a maximum of two concurrently running dynos.
By default, all applications are limited to 100 dynos. Additionally, a process type can’t be scaled to more than 10 dynos for performance dynos.
Submit a request to raise this limit for your application.
Processes / threads
The maximum number of processes/threads that can exist in a dyno at any one time depends on dyno type:
eco,basicandstandard-1xdynos support no more than 256standard-2xandprivate-sdynos support no more than 512performance-mandprivate-mdynos support no more than 16384performance-landprivate-ldynos support no more than 32768
These limits include all processes and threads, whether they are executing, sleeping or in any other state. Note that the dyno counts threads and processes towards this limit. For example, a standard-1x dyno with 255 threads and one process is at the limit, as is a dyno with 256 processes.
Build
Concurrent builds
Heroku only allows verified accounts to run builds of multiple apps across an account concurrently. Verified users without an established payment history can create up to 10 concurrent builds at one time. Verified users that also have an established payment history can create up to 300 concurrent builds at one time.
Git repos
Users are limited to a rolling window of 75 requests to Heroku Git repos per hour, per app, per user.
The uncompressed size of a checkout of HEAD from the repo, combined with the size of restored submodules, cannot exceed 1 GB.
Slug size
Your slug size is displayed at the end of a successful compile. The maximum slug size is 500 MB; most apps should be far below this limit. Once a slug size reaches 300 MB we will warn about larger slug sizes having the potential to cause longer boot times.
Slug compilation
Slug compilation is limited to 15 minutes.
Heroku Postgres
Dataclips row limits
Dataclips can return up to 100,000 rows.
Dataclips data limits
Dataclips can return up to 100mb of data.
Dataclips query limit timeout
Dataclips will cancel queries after 10 minutes.
Basic, Standard, Premium, and Enterprise tier limits
The limits associated with each Postgres plan tier are described in the Choosing the Right Heroku Postgres Plan article.
API
Heroku API limits
Calls to the Heroku API are limited to a rate of at most 4500 calls per hour.
Network
Network Bandwidth
Network bandwidth is soft limited at 2TB per app per month.
Enterprise Teams
Membership Limits
Enterprise Team memberships are limited to:
- 25 members for non-enterprise accounts
- 500 members for enterprise accounts
Other
Maximum number of SSH keys
All accounts may have a maximum of 50 SSH keys associated with their accounts. If you need more than this you should look into using the Build API.