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    Architecture

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    Johan Harén
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    This article describes the architecture of the Halon platform.

    How messages are processed

    SMTP Flow Configured per HSL script Process Description
      CONNECT Server (listener) CONNECT context smtpd IP based filtering in order to check against e.g. IP reputation services
    HELO EHLO HELO Server (listener) HELO context smtpd Allows verification of the HELO and EHLO domain.
    AUTH AUTH Server (listener) AUTH context smtpd Used if client tries to authenticate (SASL).
    MAIL FROM MAIL FROM Server (listener) MAIL FROM context smtpd Filtering in order to control relaying, or verify SPF etc.
    RCPT TO RCPT TO Domains RCPT TO context smtpd Filtering in order to control relaying, prevent backscattering.
    DATA DATA Domains DATA context smtpd Processing the actual mail message, such as spam and virus rejection.
      Pre-delivery Global Pre-delivery context mailqueued Before a message delivery attempt (unless in-line delivery is used).
      Post-delivery Global Post-delivery context mailqueued After a message delivery attempt (unless in-line delivery is used).

    Disk layout

    In order to provide reliable updates and simple maintenance, each Halon platform node consists of four partitions, listed in the table below.

    1. The recovery OS takes care of the actual software update procedure (overwriting the system partition). It is always read-only, and never updated in itself.
    2. The system partition (mounted read-only during normal operation) contains the actual Halon software, which is a complete software distribution (operating system, based on FreeBSD). The system partition completely overwritten with each update.
    3. The configuration partition contains the revision-managed configuration file. This partition is, of course, not touched during updates.
    4. The storage partition is used for all large files and heavy write operations, such as mail queue, swap, virus definitions, logs, and much more.
    Partition # Partition label Mount Function Read/write Size
    1 halonrecovery   Recovery OS Always read-only 20 MB
    2 halonsystem / System Read-only 250 MB (approx.)
    3 halonconfig /cfg Configuration Infrequent writes 20 MB
    4   /storage Storage and swap Heavy IO Configurable, can also be on a separate disk

    Growing storage disk

    If you're running on a hypervisor, you can grow the storage disk under Hosts -> System -> Disks after you have expanded the disk in the hypervisor.

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