Kevin McConnell
c1600a99e2
In order to control routing dynamically, we need to expose some Beamer information to the proxy. The `beamer_writer` value is used by the proxy to keep track of which node should receive write requests. When it changes due to a failover, the proxy will update after seeing a new value in this header. We provide this to the proxy in the `X-Writer` response header. The `beamer_last_txn` value will be used to control writer pinning. Setting it in the cookie here is the first stage of this. The second stage will be to catch situations where a reader gets a request where this header value is set to a large value than the reader has seen; when that happens if means there's a risk of reading stale data, so rather than serve the request we should request the proxy to reproxy it back to the writer. We also set `X-Kamal-Target` in the response to match the `X-Kamal-Target` that was set in the request; this lets us see which proxy target served each request, which is useful for diagnostics.
40 lines
1023 B
Ruby
40 lines
1023 B
Ruby
module LoadBalancerRouting
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extend ActiveSupport::Concern
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ALLOWED_PRAGMAS = %w[ beamer_primary beamer_last_txn ]
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included do
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before_action :set_target_header, :set_writer_header
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after_action :set_transaction_cookie
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end
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private
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def set_target_header
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response.headers["X-Kamal-Target"] = request.headers["X-Kamal-Target"]
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end
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def set_writer_header
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if ApplicationRecord.current_tenant.present?
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response.headers["X-Writer"] = pragma("beamer_primary")
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end
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end
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def set_transaction_cookie
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unless safe_request?
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if ApplicationRecord.current_tenant.present? && Account.sole.present?
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cookies[:last_transaction] = { value: pragma("beamer_last_txn"), path: Account.sole.slug }
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end
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end
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end
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def pragma(name)
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if ALLOWED_PRAGMAS.include?(name)
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ApplicationRecord.connection.execute("pragma #{name}").first&.values&.first
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end
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end
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def safe_request?
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request.get? || request.head?
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end
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end
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