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When a node leaves a network or the cluster, or memberlist considers the node as failed, NetworkDB atomically deletes all table entries (for the left network) owned by the node. This maintains the invariant that table entries owned by a node are present in the local database indices iff that node is an active cluster member which is participating in the network the entries pertain to. (*NetworkDB).handleTableEvent() is written in a way which attempts to minimize the amount of time it is in a critical section with the mutex locked for writing. It first checks under a read-lock whether both the local node and the node where the event originated are participating in the network which the event pertains to. If the check passes, the mutex is unlocked for reading and locked for writing so the local database state is mutated in a critical section. That leaves a window of time between the participation check the write-lock being acquired for a network or node event to arrive and be processed. If a table event for a node+network races a node or network event which triggers the purge of all table entries for the same node+network, the invariant could be violated. The table entry described by the table event may be reinserted into the local database state after being purged by the node's leaving, resulting in an orphaned table entry which the local node will bulk-sync to other nodes indefinitely. It's not completely wrong to perform a pre-flight check outside of the critical section. It allows for an early return in the no-op case without having to bear the cost of synchronization. But such optimistic concurrency control is only sound if the condition is double-checked inside the critical section. It is tricky to get right, and this instance of optimistic concurrency control smells like a case of premature optimization. Move the pre-flight check into the critical section to ensure that the invariant is maintained. Signed-off-by: Cory Snider <csnider@mirantis.com>
The Moby Project
Moby is an open-source project created by Docker to enable and accelerate software containerization.
It provides a "Lego set" of toolkit components, the framework for assembling them into custom container-based systems, and a place for all container enthusiasts and professionals to experiment and exchange ideas. Components include container build tools, a container registry, orchestration tools, a runtime and more, and these can be used as building blocks in conjunction with other tools and projects.
Principles
Moby is an open project guided by strong principles, aiming to be modular, flexible and without too strong an opinion on user experience. It is open to the community to help set its direction.
- Modular: the project includes lots of components that have well-defined functions and APIs that work together.
- Batteries included but swappable: Moby includes enough components to build fully featured container systems, but its modular architecture ensures that most of the components can be swapped by different implementations.
- Usable security: Moby provides secure defaults without compromising usability.
- Developer focused: The APIs are intended to be functional and useful to build powerful tools. They are not necessarily intended as end user tools but as components aimed at developers. Documentation and UX is aimed at developers not end users.
Audience
The Moby Project is intended for engineers, integrators and enthusiasts looking to modify, hack, fix, experiment, invent and build systems based on containers. It is not for people looking for a commercially supported system, but for people who want to work and learn with open source code.
Relationship with Docker
The components and tools in the Moby Project are initially the open source components that Docker and the community have built for the Docker Project. New projects can be added if they fit with the community goals. Docker is committed to using Moby as the upstream for the Docker Product. However, other projects are also encouraged to use Moby as an upstream, and to reuse the components in diverse ways, and all these uses will be treated in the same way. External maintainers and contributors are welcomed.
The Moby project is not intended as a location for support or feature requests for Docker products, but as a place for contributors to work on open source code, fix bugs, and make the code more useful. The releases are supported by the maintainers, community and users, on a best efforts basis only. For customers who want enterprise or commercial support, Docker Desktop and Mirantis Container Runtime are the appropriate products for these use cases.
Legal
Brought to you courtesy of our legal counsel. For more context, please see the NOTICE document in this repo.
Use and transfer of Moby may be subject to certain restrictions by the United States and other governments.
It is your responsibility to ensure that your use and/or transfer does not violate applicable laws.
For more information, please see https://www.bis.doc.gov
Licensing
Moby is licensed under the Apache License, Version 2.0. See LICENSE for the full license text.